Collections were one of the first reason I went to Hashnode (before it was named like that, but Devsomething), to be able to share stuff in a unique place, then share it to a broader audience (LinkedIn, Twitter), and be able to retrieve it easily, no matter on which account I am.
The new bookmarks haven't removed collections, but made them unusable. In short, you can still retrieve your old collections (like https://hashnode.com/@sportebois/collections), but it's really not as convenient.
I guess I could come back to plain old bookmarks, but I do have different use-cases for bookmarks and collections (the main difference one being the lifetime of the item. I bookmark long-lived links I want to retrieve in months from now, and use collection as an interim stuff: a convenient way to retrieve links in a few weeks (which is PITA on Twitter or LinkedIn). And when I search back in collections for a link a few times, then I bookmark it (already time many times).
I guess this is very specific to me, but my point is: collections were really useful, to a point I might even consider sharing much less on hashnode, because this first-class way to keep track is no longer there.