Short answer: Perfection is not easy.

Yes, using the above-mentioned tools makes playing easy - but we're not just playing here.

We're attempting to perfect the games to godly level of precision - which involves handling the game like if it was The Matrix - observing every slightest detail of it to gain control of it in ways that the makers never realized. We're searching for perfection.
To reach that goal, using the features provided by an emulator is irrelevant, as long as the "world" - the game - is unmodified.

It's a really huge job to produce a good timeattack movie. Sure, anyone can undo when they make a mistake - but who can spot the error that causes 0.1 seconds of delay in the movie? Who can spot and abuse bugs in games to do seemingly unearthly maneuvers?