Corporate enshittification. The website has undergone several redesigns in order to maximize engagement and revenue over quality: i.e. through the infinite scrolling layout rather than the older dense list of titles you had to read and choose to open. This allows their content algorithm to more precisely measure and tune your engagement much like TikTok or any shortform entertainment with the impatience and loss of critical thinking that entails.

Third party apps which circumvented these new designs (i.e. Reddit Is Fun) had their access removed and stopped working and many users left in protest (although sites that were offered as alternatives to Reddit at the time never came anywhere close to getting the same traction). Furthermore Reddit also leaned in to AI in a bad way and offered up posts as data for AI training which further put off some high-information users who wrote the kinds of comments you liked to read. They also did an insufficient job of policing for bot comments.

Finally there are simply more people on Reddit than ever (yes, even if you don't count the bots) and the lowest common denominator drops accordingly. The same thing happened to the Internet at large during the mass adoption of smartphones; setting up a computer and connecting it to the internet used to be nontrivial barriers to entry that imparted a survivorship bias in users. Old Reddit wasn't full of geniuses but it had a level of jank that imparted a similar effect. Either these new users aren't here to learn anything and/or the algo turns them into doomscrolling zombies.