In all truth, NASA only receives about 0.5% of the federal budget. While that is still a large amount, the VA gets roughly 1.2% of the budget. The DoD gets roughly 13% of the budget.
Not to mention some of the things that came from NASA research.
Burden of proof has yet to be established that they just "pocket" billions of dollars. Thus, it remains a conspiracy theory that holds little merit.
It's also worth mentioning that the $20 billion that NASA gets isn't all used in space research. NASA stands for "National Aeronautics and Space Administration" and the "aeronautics" part includes things like research into aircraft safety, novel aircraft designs, work on improved fuel efficiency...that kind of thing. NASA owns a bunch of wind-tunnels - one of which is (I believe) the largest in existence.
Also, it is very obvious to anyone who lives near one of their launch sites that they do in fact launch HUGE rockets on a fairly regular basis. Even if you believe that those are not reaching orbit (or whatever you really believe) - they still cost a lot of money to build and launch.
NASA's payments to outside contractors is whatever it is...the number of staff they employ is clearly what they claim it is...PLUS the staff who are faking all of these videos.
Consider things like the James Webb Space telescope - even if it's not a 'real space telescope' - they still paid a shit-load of money to have those huge mirrors ground - and they definitely build all of the mechanism to unfold them - and the money for a rocket large enough to convince their neighbors that they really are going to launch it.
With all of those expenses, it's REALLY hard to see how they can be "pocketing" very much of it.
Also - who are the "they" who are doing the pocketing? Employees of NASA? They seem to be paid the standard rate for engineers, etc. The management?
I just don't see how this insanely complicated process of faking everything could possibly turn a profit at all!