[crazygringo]

Except that I haven't seen a marquee used on a web page anywhere in years. Except in incredibly specific contexts (like a long title in a music player app), it's generally considered bad UX design.

Whereas toasts are everywhere, a common, useful, established and recommended UX design pattern. So it's a genuine convenience to developers for browsers to provide it, in the same way browsers provide buttons, combo boxes, and date pickers. (Even though all of those also can be, and sometimes are, implemented in JS.)

The "good argument" to me boils down to use and convenience, and removing cruft.

[yyyk]

Well, a marquee (not necessarily the HTML element per se but the design element) is often used on news sites/forums, at least amongst those I visit currently - it's used there as a news ticker.

I could go on and argue that it's far more common than a toast (which I barely see at all. Than again I don't like PWAs and try to avoid browsing from mobile when I can). But the sites I visit are not remotely representative at all, so I could well be wrong. I guess the sites you visit are also not remotely representative.

IMHO, The fact that <marquee> was added and supported for so long (despite 'deprecation') is the best indication there's some demand for it, a better indicator than our browsing habits. Marquee is definitely more distinctive than <toast> is from other elements and better supported. So IMHO there's a much better case for including it compared to <toast>.

P.S. The browser provided date pickers are so poorly designed and inconsistent I wish they didn't provide them at all. It's something I always override when I have time to do it.