I think the issue is with how many hoops you want to jump through in order to fix BMWs, specifically.

If I'm running an auto-repair shop and I already need specialty kits and tools for more common vehicles, why am I going to invest in one for a far more niche brand? And if the number of non-dealership repair centers for BMWs dry up, the pool of people skilled in repair go with it.

It's a death spiral for the brand as a whole, in pursuit of marginal increase in dealership based repairs.