This may not hold true for those still looking after a few years, but a big part of the problem is that they just don’t know how to act, how to treat a girl, what to expect. From your examples and from what I see from my son, they’re trying to impress
the other person. Part of this is the system. There’s pressure to prove yourself.
There’s competition. When they first start to date they may not be ready, but feel obliged to do so, by their parents, their peers, whatever. And later on, they may be just plain scared due to what they see around them.