It's just a whole different way of consuming content. I like my content organized and structured so that's why I was on Reddit and now Lemmy.

Twitter/Mastodon is less structured. It's just a stream of posts, not even necessarily in chronological order nor attached to the thread. You may read something interesting and get into the whole thread of posts. On Lemmy, that would be equivalent to browsing by new, and instead of showing posts it shows all the latest comments and posts the same way. Often you'll get to a post by the discussions around it, not necessarily directly via the top level post. It's like joining in the middle of a conversation.

As to why, well, people have been using the wrong tool for the job since forever, it just happens organically. There's people on Instagram sharing stories as slideshows of pictures of just text. The same is happening on TikTok except you get some shitty overused song in the background with it. The average person tends to pick the platform by popularity and trends rather than what it does, and just do whatever is necessary to make the content fit in it.