Battery use is a pretty big concern these days; also, some users like running several things at the same time.

For the local OS and sustained workloads like video playback, yes, battery optimization is huge. For an individual app with bursty compute, less so, plus some of that inefficient code can run in the cloud instead, which is costly, but premium subscriptions can pay for it, and power plants are now colocated with data centers so power transmission cost is negligible. The incentive to be efficient is insufficient.