Why does approximately no one outside the US use iMessage then?
Yes, it's easier if you have $750 to spend and are willing to cede control to a trillion dollar megacorporation. It's impossible if you're already on a different platform.
Sometimes being inclusive means doing some work, going out of your way a little. Having to download another app is not a huge burden. The fact that kids aren't doing it is an indictment of American culture first, Apple second, adults third, and finally the kids themselves.
Effectively no human with a smartphone outside the US finds having to install an app to communicate with other people in a cross platform way a burden enough to stay with iMessage.
Either Americans are uniquely lazy when it comes to installing apps on their phone, or this argument doesn't hold any water.
A false dichotomy. One third option: there are network effects at play in America that aren't at play in Europe. Consider the relative market shares of the iPhone. US: ~58%, e.g., Spain: 25%. [1] Thus, when one boots an iPhone in the US, roughly 60% of one's friends already have this functionality. And that market share likely skews towards self-selecting groups such as teenagers. Also note that sending an SMS doesn't have as significant of a historical drawback in the US as it does in Europe. There may be some limitations, but, again, given the market share, it's unlikely one is going to reach one's SMS limit texting grandma. Thus, because US people can be more accommodating in terms of messaging with other phones without a third-party app, it's a perceptively useless install in America. Pretty much apps like WhatsApp are only used by US people with Android devices for communicating outside of the US. Otherwise, it's unlikely a US person needs to do anything other than send an SMS, and, hence, the green bubble.
That's not how it works. These kids didn't create the stigma for the green bubble. Popular culture did, big-money TV, movie and music productions did, and teens are the most susceptible.
Try finding a recent US-produced music video or hit movie/TV series that shows a green bubble (or Android for that matter, as it still has a higher market share).
Plus, by ensuring your kids use SMS instead of iMessage, you can be assured of your own ‘inclusion’ in their text chat logs through the cell carrier’s parental log.