It's literally the same reason behind reading HN. A HN with a higher ground noise but much more real-time, interactive and orders of magnitude higher bandwidth.
You just need to curate things very hard so make sure you keep enough signal above the nose to be worth it.
Signal to noise on Bluesky is about as bad as on Twitter, I think it's just that the type of platform and the format are not conductive to good communication. It's the equivalent of panning for hours and hours to find a tiny bit of gold, it's just not worth the time you waste on it.
Twitter was great for getting intermittent announcements. Not so great at facilitating a respectful dialogue.