I'll give another way to look at it. Good design is by no means the same as optimal design. A lot of beautiful designs done by talented designers end up being worse than what was before. They might be prettier, but they are very likely worse by many conversion metrics.
Don't think of it in terms of pure design. Think of it in terms of cost. Everything has a cost and sometimes good design's real cost is in user behavior. Pageviews and time on site could go down because people aren't going through so many steps to get to what they want. There are a lot of metrics that aren't that useful without the context of the ultimate conversion numbers for your site/app/product/project.
Facebook and Google are advertising companies. The financial metric they care about is advertising revenue per user and number of users. It's not much different than a SAAS app in that way. Other metrics are important, but that is the metric that pays the bills.
A beautiful design that doesn't improve the core metrics is like a multi million dollar super bowl commercial that flops. Sure, it might be really cool and well produced, but if it doesn't sell your product, you might as well light that money on fire. The net effect is the same.
The underlying assumption being something like "If you're not increasing the amount of money you make, you are of no value"
Facebook says it's values are connecting people and other helpful ideas for a reason. If they created a design that helped people connect more fluidly, it'd still be valuable, even if it didn't increase their revenue. I find your comment a bit cynical and oversimplified.
Well, I don't think it's a completely binary money or UX type decision, but I do know that working at a larger scale of users shifts your priorities significantly.
For example, I worked on a website that would sometimes process as much as a million dollars in donations in a single day for a nonprofit. If the site went down for even a half hour, that could be tens of thousands of dollars in missed donations. That is like someone not getting paid for almost a year.
We had a cool autocomplete feature that went out and due to a bug that made it past QA caused a on of DB queries and took down the server. It was maybe a better user experience, but the way it was implemented would cost too much in reliability for it to be worth it. The team reengineered the concept until it worked at scale.
A lot of hackers I know who aren't working on that scale don't worry about QA or bugs so much because hardly anybody is using their software and it's not mission critical. When you have millions of people touching your software and it is processing millions of dollars in transactions, the metrics that matter are different.
I am sure Facebook cares about UX, but they are a publicly traded company and if a slightly better UX delivers a significantly worse ad revenue number, that isn't just sort of bad for investors, it's bad for the employees job security (and stock value), it's bad for the advertisers who can't get the same ROI on their ad spend, and ultimately it's a little bit bad for the end users because if "good UX" doesn't make money, then over the long haul, Facebook will learn to not invest in "good UX".
I think the scale that Facebook's engineers are working at is a lot bigger than most of us can easily appreciate.
Here's a hypothetical counterpoint to your proposition here:
A search company makes money from ads, which are unobtrusive text links which are clearly separated from search results.
The search company is forever trying to improve metrics, and in this quest, it pushes more intrusive monitoring of users, and the adverts become more and more like search results at the top of their results. According to their metrics, this is a winning move - more and more people are clicking ads, and advertisers love the stats on users.
The search company slowly starts to lose users, because they don't like the privacy issues and the intrusive ads in their search, even if more people click on them.
A few years later, the search company starts to lose its dominance of the field and hence all the money they made from more and more ads is now drying up, but every change they make to increase clicks on ads is actually having a worse effect on usage a few months down the line, even if it helps their metrics in the short term. No-one notices because the users have always been there, and this is not a primary metric or one that is easily correlated with changes.
Was this a good strategy? It was certainly a local maximum, and all the numbers went up, but was it in their long term interests?
I agree for someone like Google or FB the metric which is important is selling ads (that is their business after all), but both companies actually have two sets of users - one set are the users who read the ads, and one set are the advertisers - both are vitally important to their brand and continuing profit. Only one of those is represented in the advert CTR metric, and only one directly makes money, but both are vitally important to continuing profits.
Now you can change your metrics to try to measure user retention, but happiness and satisfaction are notoriously slippy concepts, and people often don't even know what they want before they see it and use it for a while (e.g. users of yahoo or one of the other portals would not have voted for changes to make it more like google), people hate any change, and haters are the most vocal. All those things completely skew any attempt to get numbers on customer satisfaction.
Don't think of it in terms of pure design. Think of it in terms of cost. Everything has a cost and sometimes good design's real cost is in user behavior. Pageviews and time on site could go down because people aren't going through so many steps to get to what they want. There are a lot of metrics that aren't that useful without the context of the ultimate conversion numbers for your site/app/product/project.
Facebook and Google are advertising companies. The financial metric they care about is advertising revenue per user and number of users. It's not much different than a SAAS app in that way. Other metrics are important, but that is the metric that pays the bills.
A beautiful design that doesn't improve the core metrics is like a multi million dollar super bowl commercial that flops. Sure, it might be really cool and well produced, but if it doesn't sell your product, you might as well light that money on fire. The net effect is the same.