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.

One of the hardest parts is just getting radio comms right. ICAO phraseology is supposedly standardized but when anything unusual happens then things get messy, especially if there are multiple aircraft involved.

Cars can drive around without needing to talk to other cars or controllers.