Frankly, as the OP stated, one reason to use a tor relay for direct traffic is to hide your traffic. A bit like a guy in a trench coat and fedora trying to look inconspicuous.
It's not illegal, but it's also not surprising when such folks are escorted out.
Presumably most folks neither know or care about this distinction and just block all Tor related infrastructure outright, since some of the traffic coming through is malicious.