Even manually pulling up the nose once you reach Vr isn't necessary if you just trim for a little extra nose-up. It'll eventually get off the ground with just enough speed.

Yeah temperature, wind, altitude, weight, runway slope all matter, and then there needs to be enough spare space for the aircraft to successfully take off even with engine failure in the worst possible moment. Then there's the question of fuel consumption too. Takeoff power isn't typically configured to get the aircraft off the ground as fast as possible, but to minimize fuel consumption, while still leaving enough margin in case of engine failure.

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.

And you don't need rudder input or any aileron input because of crosswind, and other bits that falls into "technically correct but not particularly relevant" territory.

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).