There is an inherent problem with microblogging sites. They don't help you understand anything. All they do is give you small blips of information, text, memes, short videos, drawings, pictures. You can't state your full opinion and it is hard to be noticed or seen because most people don't bother getting into any topic in detail. On the other hand, social news plafrorms - like Lemmy and Kbin and even Reddit - encourage dialogue and discourage toxicity.
Microblogging has changed. Now, I much prefer talking about current events on a social news platform than on a microblogging platform. Right now microblogging sites are good for art or talking about general interests and things in your day-to-day life, maybe getting some news out of them (if the algorithm wants you to because algorithms suck when it comes to news, especially in a divided society such as this one), but not much more. Plus, the "balkanization" of microblogging with services like Tumblr, Threads, Bluesky and Mastodon makes it so that you divert attention to different things in different places, while things like the threadiverse can be a hub for pretty much everything because information doesn't flow as fast as on microblogging sites so you don't lose attention very quickly.
I understood the problems with attention span that plague Twitter long before the big switchover was even a thought, it's just that I didn't think of it too much back then.
In my opinion, microblogging isn't really a conversational platform. It's a creator and audience platform. That format has its place, as well, but Twitter/Threads/Mastodon/etc. isn't a replacement for forums.
I think that's fair. Good conversations can and do happen, especially on platforms allowing longer contributions like tumblr, but when a site revolves around following people instead of subjects it makes your interactions a public performance to all of your followers. That has a huge impact on discussion quality, incentivising dramatic takes popular in your corner of the internet and disincentivising saying anything controversial.
When you combine that with poor moderation on most platforms and algorithms that promote outrage-inducing content, toxicity and cancel culture are inevitable imo. It's shit even for creators.
Thinking on it more, I think parasocial relationships should be mentioned too. If you get popular it can be difficult to publically argue with anyone without followers harassing them to defend you (and their followers doing it to you). If they do so publically, or just share what you've said, it can spread the argument to even more hostile people.