React tutorials shouldn't cover this. They're for learning React. Otherwise every tutorial for anything web based would need to include all the basics about the web too, every time.

I don't have an answer for where the best place to learn it in the course of becoming a dev. I learnt this stuff over 25 years ago when I was a teenager. The thing is, it was a necessity then. Now I can download a whole movie in less time than a poorly optimized webpage in the 90s. So while I still obsessively try to get the smallest best looking images when I'm doing frontend dev, I'm not sure it's really worth my time.

The author mentions automated tooling and I can see that being the best middle ground these days.