From the standpoint of the individual developer, you handle edge cases like this so you don't break your clients' experience.
From the standpoint of the ecosystem, broken tools are bad, and they cause individual developers to have to handle more edge cases.
If one individual developer doesn't handle these edge cases, their clients will just think they are bad. If all of the individual developers decided not to handle these edge cases in a coordinated fashion, sure, they could trigger a change. But I don't think that's how it happens in the real world.
To look back on the days of IE6/IE7, most developers didn't just stop supporting these browsers and hope that their clients would stop using them; they supported the browsers until larger forces caused their clients to shift to newer browsers.
Getting back to my original point, I think it's possible for each of you to have the viewpoints that you have, but also for rachelbythebay to say, "Sure, if I could coordinate with all other devs to stop handling broken edge cases at the same time, I would do that," and for you to say, "Sure, I can see how you would want to keep your job and handle edge cases until they are fixed upstream."