Mozilla did multiple times and is doing it, sometimes even doing the work that Google is supposed to do (see e.g. the Webcompat project [1]). The point is, this problem is basically unsolvable without having the reach of Google and thus everone (incl. Microsoft!) is forced to spoof the UA.

See also https://webcompat.com/

No company is "supposed" to do anything in my eyes; and I'd rather if they all did a lot less that wasn't defined as "produce this one very specific product that does one thing well". If anything, the agencies that are supposed to do anything for the infrastructure of the Internet are the various governments and the UN, to support an open Web. The problem is that at present the US, UK, Russia, China, North Korea, and several other key nations are trying to destroy the open Web, so it falls to companies, who are better off setting up their own walled gardens and forcing every user into the digital equivalent of the old mining company towns.

We need to stop bending to any of these groups just because they're "the big guy". If the largest Web company is building "free" and "open" stuff in an anti-competitive manner, then make sure that's painfully obvious to the end-user, make it public (i.e. an NYT article's a nice start) and then file federal lawsuits, calling on users as witnesses. The people of America beat the Robber Barons before, I don't understand the reason why we are so unwilling to do so now that they've moved to the Web. Stop spoofing, stop capitulating, stop compromising, and start fighting back.

So you're saying Google and the likes should ignore the very principles of the web that made them successful and even possible unless they're sued or regulated? That they can do whatever the freak they want without respect towards the environment (meaning both the web and economical/legal/political environment) they operate in? That's how you destroy ecosystems, economies, even political unions.

That's probably my biggest grief with many big companies today (and probably most big companies ever), the lack of respect and decency (in general). The few big tech companies I see that show a decent amount of respect (but still a long shot from perfect) are either run by Elon Musk or Apple, with Microsoft slowly but steadily digging themselves out of their rabbit hole.

I genuinely believe that the government should have long since stepped in and closed them for anti-competitive behavior, back when this all started. The way things are currently though, there's no onus on the company to be a good actor, when bad acting gets them higher market share and thus higher revenue. Hence, they're not "supposed" to do anything. But I also believe that Google, as a company, should be allowed to develop a search engine, and that's it, everything, end of story, finito, no additions substitutions or refunds. That search engine might be a damn good search engine and have an absolutely mind-boggling database, but that's all. Maybe also the focused searches like Images, Shopping, and Video. When you get to Maps, Mail, and Voice, those should be separate entities owned by people not involved in Google, not invested in Google, and who do not have a managing stake in Google whatsoever.

The problem with filing lawsuits is that "anti-competitive behavior" is typically not treated as illegal by recent US courts unless there's demonstrable consumer harm in the form of higher prices. Which there is not with products that are distributed for free...