Physical letters do not obviate scams, nor is the cost that prohibitive. I remember actual 419 scams on blue airmail all-in-one letters back in the 80s. And that was international post too.
I have an inbox, and I do not receive a lot of scam post. In fact, I don't think I received any since I lived at this address (~10 years ). We do get a few promotional leaflets every other week.
OTOH, I get hundred of spam emails every day.
The former is something which I can handle manually easily, the other is not.