Android itself takes up 9GB on my Pixel 2. 4.7GB is taken up by the apps and whatever they are storing (Chrome takes up the most, with 1GB). I also have 4GB in music.

I don't consider myself a heavy storage user but 16GB is a really easy bar to cross.

I've noticed on my iOS devices that the more storage available, even with the same amount of apps and data, more storage is taken up.

I believe it's due to the fact that apps don't clear caches as often if there's plenty of space left.

That would make sense. I believe many apps, including Chrome and Firefox, do the same thing with RAM. If it's there, might as well use it.