But it turns out a bot can look very much like a logged in paying customer, just they're paying with a stolen credit card and you'll only learn that in 2 months when the chargeback arrives...
Still not a reason to block by browser, bots don't even use them...
At any rate, based on what I've read this is a false alarm anyways, it's annoying and stupid but UA banning is not browser detection. This is more ass-covering - another commenter mentioned too many layers of abstraction which is probably closer to the mark - something broke somewhere and a customer complained, they don't have the time nor inclination, or perhaps even ability, to fix their issue, so they do the 'we don't know what's wrong, halp' thing, versus making a more robust site.
Which fits my impression of their site, shoddy service with mediocre hosting services. Superbowl/pornstar marketing though, so everyone has heard of them, in comparison to aws (you have heard you can host godaddy even if you think Amazon is just a place to buy shoes, and Amazon is both bigger and better)
Nearly every metric is worse - from spam comment removal rate to adspam rate to credit card chargebacks.
I can completely understand a web host deciding to block any browser that isn't a major one.