I've used printer paper myself in different jobs in science. I personally don't like it but I have done it when it was the only paper available. Budgets in scientific organizations are often very tight, so often nothing else is provided, and many times you do not have the direct authority to order anything yourself.
My point is that I'd view this behavior more as a consequence of the circumstances many scientists find themselves in rather than a conscious choice, though I do admit that some people may like it more than I do.
I don't have an exact preference on the kind and weight of the paper, but I do prefer notebooks with firmly bound and numbered pages like old-school laboratory notebooks [1]. My problem is that I often do long derivations or work that can span dozens of pages with diagrams, etc. If I use loose leaf paper like printer paper, I often lose track of pages or their order. I tend to label my pages extensively when I have to use printer paper. I also use binder clips instead of paper clips since they are much more secure. That system works for me but other people might not like it.
Notebooks are cool, but I prefer printer paper for short term notes. I tend to staple them together if there's more than a few pages. If I need to remember something for longer than the few weeks before I lose the sheets, I take a picture with my phone.
My point is that I'd view this behavior more as a consequence of the circumstances many scientists find themselves in rather than a conscious choice, though I do admit that some people may like it more than I do.