Because it's physical, I think you give it more weight (so to speak). I doubt you average more than five or ten pieces of physical junk mail per day, but it's not uncommon to receive hundreds of spam messages a day, or more, most of which is blocked at the server level, and most of the rest of which is blocked by your client filters. I've had my email address for about 15 years, and there are thousands of attempts per day to send to it that my email server blocks, and then when gmail picks up my mail it cuts out promotional and social stuff, as well as whatever it think is spam, and I end up seeing 5-10 messages a day total (including mail I want to see; email is not a major channel for me outside of work any more...).
Further, that physical spam is really, really well targeted compared to email spam. You may not care about most of it, but at least it has something to do with your real life (mostly coupons and advertisements for local businesses, if yours is like mine).