Well, collections are not completely deleted as pointed out by Sébastien Portebois and Jan Vladimir Mostert.
At this stage, we want to focus on things that are the core functionalities of Hashnode (writing, asking and profiles). The main purpose of the collections was to organize Hashnode data at the profile level. Some of you like Jan Vladimir Mostert, Sivabalan, Kleo Petrov actively used it but majority didn't.
We've been getting a lot of feedback from the time we have disabled collections. There's no final decision on its status as of now. We're brainstorming many cases like how to make it quickly accessible if it comes back. We'll keep you posted on this.
Thanks for starting this discussion thread. :)