It really isn’t, and especially not when one of the browser’s unique selling points is its multi-browser extension compatibility that no other browser offers.
Also some of us simply don’t want to learn new UIs and/or risk dealing with an “AI” infused alternative if we have a tool that already Just Works. Switching away from Just Works sucks.
The worst part about opera dying was the email client imnho - and it wasn't trivial to find a replacement.
I'm not sure what I'd seek in a browser I'd pay for - but it would be features not present or great in foss browsers.
Maybe email, podcast, rss client, a modal vi like browsing (like vimperator, but first class), a good reader mode/style override, proper editor for text input (like "it's all text"), automatic force support for select text, save as... for images)...
But whatever would be useful enough to pay for, would likely be a pain to lose.