They only care about monetization. If they can achieve that easier with a new UI you know they're going to do that. Old.reddit.com and the current www.reddit.com are both expendable if they can make more money without them. This is the new, publicly-traded corporation Reddit. Tradition be damned, they will make their money in whatever manner pays best.
If people thought algorithms were bad before, they’re about to get a titans times worse for Reddit.
I have a self-hosted troddit instance I use to check up on smaller communities, or to replace Reddit.com queries from search engine results with abs when it loads the front page vs the Reddit.com front page is vastly different.
There’s no surprise why they got rid of the api, because they’re playing with engagement and need more direct access.