The market cares. In my experience it’s harder to make your boss care.

It’s often been hard for me to make coworkers care as well which is even more frustrating.

Unless your job really prioritizes performance and builds in benchmarking people often focus on finishing a feature as fast as possible and ignore performance (and accessibility, bugs, UI polish, etc.)

Experiments demonstrate that increasing web search latency 100 to 400 ms reduces the daily number of searches per user by 0.2% to 0.6%

It obviously depends a lot on what you do, but often that doesn't matter.

Do you think most websites are hitting 100ms? You are picking silly numbers. The real world case is more like 500ms vs 2.5s. The pingdom numbers suggest that is more like 5%. It's very common for pages to take over 5s to load. That is a huge bounce multiplier. I just did a search for "sony lens" on fb marketplace, and it took about 2s to load the page. This is a very very optimized page, it got some results at the top within 500ms, which was probably enough to fill above the fold on mobile (and thus seem like it was finished). however the broader search to fill the results took about 2s. When I worked at eBay searches took 2-3s routinely if they weren't warm. Getting to 100ms for a lot of very important ecommerce pages, which are critical in terms of bounce rate sensitivity, is a real engineering challenge that millions of dollars are spent on. Imagine if eBay could get 3% lower bounce on their search pages, delivering that would make multiple careers.