"Why would any of this stuff matter to them?"

Back when I started, both the BASIC and Common Lisp camps had heuristics on helping the compiler generate more efficient code. The reasons are similar to today: increase throughput for scaling or customer experience while simultaneously reducing what you spend on hardware and/or electricity. Lean, easy-to-manage setups can also sometimes let you afford extra personnel to build stuff faster.

There's definitely a cut-off where micro-optimizations wouldn't be necessary. A lot of efficiency gains are simple, though. Just gotta consistently use what you learn.