An airplane will take off when it is properly configured and it hits a certain speed. It's simple aerodynamics/physics. Pilots are there to react to failures and unexpected events.
I just followed what my CFI and Cessna's manual for the C172 said (which iirc was giving input to rotate at 55kts).
It wouldn't be that hard to fully automate a flight from gate to gate when everything works perfectly. But the various failure modes, human error like airport vehicles entering active runway, all that requires human backup. Self-driving car can just stop to the side of the road and turn on emergency lights if its engine fails, with a plane things get much more complicated.
Cars can drive around without needing to talk to other cars or controllers.
It's fun to see/feel planes do stuff "on their own" (eg making them oscillate, or level on their own, or feeling ground effect, or even your own wake on steep turns) but it's not something you'd want to rely on (maybe with the exception of ground effect on short field takeoffs, but I digress).