The platform itself has to be constantly maintained, which requires a crew. Military or at least cruise ship with disciplined crewman, rather than anything civilians can be trusted or expected to maintain.
Ultimately, it's a question of building a floating thing, and keeping it floating. This strikes me as not-too-hard, compared to the usual space problem of trying to hold oxygen in a bubble in a vacuum. You just need a sustainable way to 'recharge' the balloons; that really just means filtering lighter gasses from the air and pumping them in faster than they leak out. The Venus atmosphere is primarily CO2 with a bit of nitrogen; the game is then filtering out CO2 and filling the balloons with nitrogen. Coincidentally, we have people putting lots of thought into efficiently filtering CO2 from air already...
The general idea of colonization of other planets is in general much farther away than your average tech billionaire wants us to think :)