Maybe things have changed now or I was just a bad react dev but the way hooks works kinda force you to have many child one-off components to not trigger rerenders in the whole component when only a small part was connected to that part of the State being updated. Having all these one-offs components in different files was painful.
Unfortunately some of us work with other people, and refusing to let them merge code we don't personally agree 100% with is a great way to stop working with other people :)
I also don't really see why this is a positive. If you have too much in a file, then split it off? It doesn't fundamentally add or subtract and complexity either way.
I think Svelte likely has a lot of benefits over React but I feel like this is a negative. It's easier for locally of code to keep related components together, and they can always be put into their own files later.