In the car industry this is the case because there is a direct incentive for the company to make a vehicle lighter.

A single kg is enormous likely saving tens of dollars per car, which sounds like nothing, but if a million of these cars are made the cost saving are in the tens of millions.

What does a software company save by their software running 10% faster on user hardware. Exactly nothing. In the case of apple they even have some incentives to make their software worse to get people to buy new devices.

The curse of software engineering has always been that there is very rarely a reward for your software being better. Software companies mostly make it on features and "good enough" stability.