[unknown2374]

The platform is the web, not the browsers themselves. The web is an open platform, while some browser push for proprietary features. This is not like Windows vs Linux where each of those OSes are separate platforms, and supporting both can be difficult.

[mgkimsal]

supporting multiple browsers can be difficult.

if you push out some purist code that is "supposed" to work to some spec, but it doesn't work... you have to start making decisions about which path forward to take.

outside pure code, you still have to deal with testing/verifying/confirming, then committing to that for each version of the browser on multiple platforms.

Providing actual strong positive and ongoing support for your system on specific browsers and platforms is generally better than "well... we wrote to the published spec, the problem is every browser vendor sucks and they need to conform to my understanding of specs". That ain't gonna happen.

To be clear, I don't think most companies actually put a lot of effort behind their 'support' of just one browser (years ago when it was IE, now when it's chrome).

[shadowgovt]

If the platform is the web, but a standards-compliant site can work in Chrome but not Firefox, the issue isn't standards compliance.

And it's up to the individual site author whether retaining that last chunk of Firefox-only (or Edge-only, or Safari-only) users is worth the cash outlay to test on those platforms. I've done multi-browser development; it adds significant friction to the process, especially if one's testing infrastructure is rocky (and most are, and it costs resources to do better than rocky).