> what it is about a foreach that you think would do a better job than a syntactical for-loop

It depends on the language. For example, an optimizing compiler can optimize the shit out of a for-each loop, but can only go so far in a for-loop. For example, in a for-loop, you can "skip around" the indices, and even go backward after going forward, while in a for-each loop, it will always go one-by-one, and the compiler can rely on that fact. Even the CPU can probably optimize it better since the data access will be more predictable.

Not only that, but a code reader can rely on this too. If you only use a raw for loop when you're skipping around, then the reviewer / future reader can slow down to understand what's happening here. If you use raw for loops for the for-each case, now the reader has to slow down on all your for loops. It's similar to the reasoning for "const everywhere": if you don't mark variables const, I need to figure out as a reader whether the variable is modified later, and that slows me down and increases the mental load of reading a function.