I think it's a simple reflection of the desire for freedom. Like a metaphor carried out into an experience...

I also think it's a central theme in LD'ing desires because it's entirely safe to do within a lucid dream. There's a fear and hesitance associated with skydiving, paragliding, hang gliding, and so on, not to mention a cost in time and money, that's not associated with flying in a lucid dream.

The fact that it's such a central thought in all our minds though... perhaps it's an indication of an archetype?

On a side note, are people aware that commercial space flights offering weightlessness are real already??!?!

My guess is that within 10 years they will be something fairly common i.e. affortable. (For middle America, that is.) but right now they're already available for the right price. Effin' unbelievable!!