Co-worker took his acura integra to an independent "honda" shop in 1990 looking to get work done. They were unaware of the connection. (Acura was born in 1986.) He went elsewhere.
There's a toyota-only shop near me, seems especially into tacomas from scanning the parking lot.
One specialty that never goes stale is the saab/volvo guy. There may be some snobbery on the clientele that demands a specialist... in fact, I hypothesize that the "need" for a specialist causes some to get a saab/volvo in the first place. You know the type: middle management, loudly blabs about how they're taking the afternoon off b/c their car's in the shop. Wonder how these mechs like the FWD ford volvos and the saabaru/trailblazer mongrels.
There is still an "autopart international" store near me but they're closed to the public: jobber delivery only.
I was trying to talk my dad into a subaru wagon in the late 1980s, he had a ford fairmont at the time. No way, said he, as he would have to get a metric wrench set.
Who knows, maybe the big 3 going metric in the early 80s helped scare mechanics into the tool investment.
I bet also the 30 MPH crash test requirements of 1980 got rid of the last wierd english sports cars and other oddball freaks, mainstreaming foreign cars enough and shaking the losers out making it was worthwhile to learn the makes remaining.