What you're describing is fully observed in education. The scale of your evaluation has to have an odd total of numbers and a limited number of choices. 1-2-3, for example. That means that each digit sends a strong signal. 1-2-3-4 means the 3 is the non-controversial choice. Average, so to speak, and you don't want average in your evaluation. You need to adequately grade stuff here, and giving most things an average grade is a weak signal that prevents you from differentiating.
When you grade by competency (not by knowledge), you also assign a written description for each grade. That helps a lot. I think those platforms are keenly aware of those facts I just described, and are trying to boil them down to simple actions for users, that impart large signal, and that respect the cultural norms of evaluation. That's why Letterboxd has a 5-star with half-stars rating system, but also has a like button.
When you grade by competency (not by knowledge), you also assign a written description for each grade. That helps a lot. I think those platforms are keenly aware of those facts I just described, and are trying to boil them down to simple actions for users, that impart large signal, and that respect the cultural norms of evaluation. That's why Letterboxd has a 5-star with half-stars rating system, but also has a like button.