Because modern websites are unusable on mobile; it's a feature and not a bug.

I've been using Firefox on android for over a decade, including for YouTube, and maybe once a year I encounter a problem where I need to use Chrome for a specific website.

Seconded, except instead of once a year it's literally never

We're only discussing one particular website, though, aren't we?

Except for on the TV (where I use SmartTube), all of my Youtube activity is done with web browsers.

Otherwise: On both big computers and with my pocket supercomputer alike, that means Firefox and uBlock Origin. It works quite well for navigating Youtube's website and watching videos.

An old iPad that I have suffers from Apple's deliberately baked-in lack of choice, but it does handle Youtube's website very well with Safari and AdBlock.

It has been a very long time since I've used Youtube's app on any device at all.