Why? Might as well ask why they go to bars, or socialize at all. If you don't get it, then nobody can answer you.
I happen to use twitter as a live RSS replacement. For at-a-glance news and tech titles, it's great.
this is pretty close to how I use it as well. It's a great way to keep up with a lot of stuff and dive deeper into the things that look interesting.
Can I call this linkbait? As someone who actually spends quite a bit of time working to understand why people use Twitter, this came off more as self-promotional wankery and no discernible insight.