A generic anime-style face is really simple to draw while still being highly expressive which helped it gain popularity in comics, illustration, and animation, but it's also really flexible. There's a lot more variation in anime faces than some people think and artists can invest the time to be fancy or not according to time/budget.
The abstraction also means that you can change things up for emphasis (really exaggerating features, pushing extreme expressions, or switching art styles entirely) without it being as jarring as it would be if the characters were photorealistic