It's because the UX for them is awful and takes up valuable real-estate unless you put them in a folder that's nowhere near your toolbar in which case you will never see them again, especially after a Mozilla update corrupts them, leaving you without the URLs you so carefully curated and with a vague sense of regret that you trusted one of the most important things (your memory) to a company that gets the largest majority of its revenue from search engine deals and the other tenth for a half-thought out proprietary bookmarks replacement they force you to waste hard drive space with.
I use the bookmark bar in Chrome but edit all bookmarks to remove their title… so I have a bar full of favicons, which is enough to have one click access to most sites I use.
> unless you put them in a folder that's nowhere near your toolbar
Hum? My bookmarks toolbar is full of folders. Some are of the "open all and close each when there's nothing interesting" kind, others are of the "will probably be useful later" kind.
In firefox, you can configure the bookmarks toolbar to only show on the new tab page, which is super useful because it doesn't steal screen space on your normal tabs.