I often wonder why some men do it...especially without thinking it through....

Firstly you will put the girl on the spot in public..leaving her embarrassed and possibly humiliated..

Secondly she could say NO.. Leaving both of you embarrassed and humiliated...

Because, if you're not sure someone wants to waste their entire life on you, why not try to embarrass them into it?
Many years ago I was at a party; we were all given champagne and told to wait expectantly for an important announcement. A couple we knew were absent from the room. A few moments later the woman came back into the room looking embarrassed and said "nothing to see, get back to having fun, put some music on". A few years later they did get engaged, but this was not the way to do it.

We agree the guy is an asshat. I’d posit he got the attitude from his mother. That young woman needs to run away fast because it’s only going to get worse.

Like other's have said, social pressure on her, or his ego wants to be centre of attention, or both. Either way it is something she might clarify if it bothered her.

I wonder if she said yes, and whatever she said, how she felt after? I read she was embarrassed; was that because of surprize, or was it something else which made her uncomfortable? That's the question she needs to answer, and resolve, or it could affect her entire life.

Perhaps he wasn't confident of her answer being positive so he used social pressure to make sure she said yes instead of no. That's manipulative and dishonest and she would be wise to rethink her answer after having some time to mull his proposal over after the 'surprise'.

A place special to them both,quiet,secluded,what if she said NO!?