Not to mention, why on earth would I ever operate a TOR relay or exit node on my home internet connection? Maybe if I could guarantee that it could only be used by journalists or political dissidents, but everything else? No.
I don't need the authorities at my door every few weeks wondering why some of the most deplorable internet traffic of all time is coming from my house.
Relay nodes don't pose much risk and help mask/blend your own Tor traffic.