No legal issue ? The aerial pictures of some countries are protected by copyrights.
Also, the pictures of approximatively 90% of the globe are just horrible.
Even for detailled places, the various pictures differ in terms of lights, colors, and even seasons, which makes some places look really weird.
Talking about seasons, there's only one available for each area.
And there is no night pictures as well.

For the moment, and for at least the 10 next years, photoscenery is not a suitable solution.

So how does the program know to edit out those aircraft sitting on the tarmac?

There's no reason to have photoreal scenery as a constant stream.  Until the size of the sim is so large that we can't reasonably keep it on our systems, it won't be feasible to have that kind of setup.