We may have lost the go to auto electric shop that can rebuild our flathead generator but Rusty is still doing speedometers. I'm going to say cost and finding people willing to work on starters, generators, and alternators in a small shop where everything you work on might be different than the last thing. You start out the day rebuilding a 9N Ford Tractor starter, then rebuild a 7 series BMW starter and then dig into a marine alternator off a sailboat that was shipped in from the far side of the country. That takes a lot of knowledge and skill. Then you have to deal with the guys who tell you that they can get for way less at O'Reilly's or off Ebay. We are going to loose more small specialty shops as time goes by. 30 years ago I thought that if I just had the money to buy a brake lathe and the equipment to rebuild cylinder heads I could make a pretty good living in a cubby hole shop. but I don't know if that holds true today.
It is good Rusty is going to carry on doing speedometer repairs, though you can see from what Mr48chev says a reason why he may have taken the decision not to repair starters and alternators anymore.
Got a guy in nearby Chattanooga owns a third generation automotive machine shop. Three employees and his wife taking care of the phone and the books. He used to build and race vintage dirt cars but doesn't have time for it anymore. Still builds engines for hot-rodders, but with all the manufacturing in the area, he makes more working on OT forklift heads than all the hot rod stuff. He is reaching the age he wants to retire but he can't find anyone willing or able to buy the business. When he's gone, the local hotrodders are going to be hurting, for sure.