At best the quality of their recommendation system has dramatically declined. At worst they're intentionally favouring different stuff. In between there are slightly more palatable (than the worst case) options, such as that they're favouring overall popularity of content more over your individual preferences, but in any case all I know is that it's turned from a relatively pleasant experience to pushing content in my face that disgusts me.
I've also written recommendation systems. In fact, I've written one I used to run on top of Twitters API. And so I know from first-hand experience that it's trivial to get better quality recommendations more aligned with what I click on than what I'm currently getting. Something is seriously wrong, whether accidentally or intentionally.
I spend less and less time on Twitter, and it's less and less enjoyable. Unless it changes drastically I won't still be there very long.