Writing code with performance in mind will get you there without any optimizations whatsoever. It's not about 12% speed up anymore, we're not living in the 70s. It's about not wasting orders of magnitude because of poor design choices.
There are clear and real incentives they are just more visible in the cloud where you pay for your hardware. Or in traditional workstation software where there's also market competition: "do that 10 times faster than the competitors and we'll talk".
It's true that with the Web the incentives are week. Sure, you'll lose some 10% of your potential visitors to frustration, but who cares if the traffic grows expectations are exponential.
Unfortunately not clear enough. Compute is cheap enough that company can easily run 10 or 100x less efficiently than it could with little extra work, because the cost barely registers when compared to revenue or salaries.
(Even working in a small company I've seen situations like someone asking, "are you folks still using the XYZ VM, because it's burned a kilodollar this month", and we're all like "a what machine? sure, shut it down". It was needed once, then forgotten about, and it took a while before anyone noticed.)