I think we lack information on what really drives the OP to do this to say anything like that. Though I was speaking about proposing like that in general. Not necessarily the OP. However because he wants to pop the question on stage, we could assume that this is a case of attention seeking. Doesn't have to be intentionally or the main reason, but it's there.
Anyways, you're contradicting yourself. You say they choose to do it like that in front of thousands of people because they feel it's romantic. At the same time they interrupt whatever the audience was doing and focus their attention on you to witness your major event. The whole attention part is intertwined with proposing in front of a mass. You can not magically cut it out.
Attention will always be part of it, regardless of your reasons to do so.