The more features in browser engines, the fewer platforms the browsers work on.
In fact, Chrome originated as - and a lot of its code structure post-Blink-fork still signifies it as being - a meta-platform of its own with a WebKit port to it.
May not be the best example since Haiku's browser is often cited by people as a big reason they can't use it as a daily driver.
I mean, if a platform doesn't support something, I wouldn't expect the browser to support it. Even if they decide that it is too hard to support a particular feature on a particular platform, doesn't mean they have to simply abandon the platform. They just don't support the feature.