Why would a guy be madly in love and obsessive over a girl but not ask her out?

Because it´s just a fantasy for him that would be destroyed if it becomes reality. It´s like a stalker that just wants to be near a person but not part of their life.
The other option he´s not bold enough to ask out especially if he´s younger not experienced with dating asking out a girl he likes is a big step for a guy if he´s not very confident in general. It could be that he thinks the feelings aren´t mutual and before he comes of weird trying to ask out a girl that doesn´t like him he tries to live with the feelings.
I was in this position once. Most likely, he's abit anxious about asking her out.
Afraid of rejection. Especially if she doesn't like him.
Because he’s manipulative
Opinion
5Opinion
Maybe complicated situations or can't trust her
Baf vibes. He's seen this landmine before.
He's incredibly shy and can't overcome it.
Fear of rejection.
Low confidence
Superb Opinion