I'm having this feeling way before the whole API story came out. At least the bigger subreddits were getting repetitive and boring, take AskReddit for example, in the past years you had the same 3 questions about dating, celebrities and what to do with with $ 1 million and every combination of that.
Some subreddits staid engaging and diverse, but most are just repetitive echo chambers.
Idk why, but this whole thing gives me similar vibes as the Turkish coupe from a couple of years ago.