With cars specifically, shops get paid to replace the blower whether or not it fixes the problem, while troubleshooting doesn't really pay. As a result there's

With cars specifically, shops get paid to replace the blower whether or not it fixes the problem, while troubleshooting doesn't really pay. As a result there's a significant incentive towards scattershot parts replacement as a diagnostic tool. I'm not saying it's done out of malice, but incentives drive behavior. You'd probably only develop solid diagnostic chops in the shop if the shop placed "bids" on fixing an undiagnosed problem, betting they can figure it out & fix cheaply.