I expect that they had something break on it and decided that it wasn't worth the time spent fixing it, so they just blocked it so more users didn't run into it. A simple message may be annoying to them, but at least they have a straightforward workaround then.

I mean, don't get me wrong, I use Firefox on both mobile and desktop, but it's not too hard to see why they'd do a cost/benefit analysis like that. No one company is in the business of trying to do antitrust work, to avoid a browser monopoly, and that'd be the reason why it'd be important to have competing browsers.

Something didn't work on Firefox and the dev didn't get permission to work out how to fix it as it was uneconomical compared with just disabling firefox