Many implementations of caches set a desired maximum size and purge unused entries as new entries come in. It’s hard to pick the “right” cache size for a phone these days. My phone has about 84GB of unused space which is just doing nothing, so I don’t mind if every app uses a gigabyte or two of cache when they need it. Someone still running on a 32GB phone will obviously think otherwise. Manufacturers like Samsung disabling adoptable storage makes the situation worse.

Devs could make these sizes configurable, but most users don’t know what that means. There’s a good chance they think caches are a waste of space (because clearing caches makes everything slower, but doesn’t break anything) and you’d risk people setting unreasonably low cache sizes and ruining the app experience.

When you’re running out of space, Android should clear out caches as it needs to free up storage. Unless you’re running into space issues (or general app issues), you generally shouldn’t be clearing caches. If you still have a few GB of storage available, u used cache space isn’t harming anyone and clearing it will only make apps download the content at a later point.