As a former mechanic, I can explain this a bit. Dealer parts departments aren't really setup for retail sale, they are mainly there to support their shop and commercial customers. I worked at an independent shop; but via fleet contracts we bought a large volume of OEM parts from the local Ford & Toyota dealers. The counter isn't manned because 80% of the parts go to the dealers shop, and the other 19.9% go to commercial buyers.
I would call up the dealership parts department and order something, they would either deliver it or let me know what the ETA was. All net-30 terms, and a stupidly low friction process. Even the chain parts stores have separate phone lines for commercial customers, I never had to hold when buying from Advance Auto b/c there was a different commercial number that they only gave to commercial customers. The garage mechanic isn't really the focus of even the chain parts stores, they make their money on commercial customers.
However, I'm glad they at least maintain the retail friendliness that they do. Try walking into your local Fastenal or Grainger without a commercial account, some of their stores just won't sell to the public. Dealer parts departments have a very similar model to a specialty industrial supplier, where retail sales aren't enough of a priority to really bother with.
And frankly, retail sales take a lot of time for them, since the customers need a lot more help. Half the time, if I was calling I already had the part number available and knew if they needed the last 8 of the VIN number and a $500 transaction only took 2 minutes of the parts managers time.
It isn't a conspiracy, they just prioritize their high value customers way more. Same applies in software. I get way better support from our specialty ERP provider than I do from Google. We pay decent money to Google, but they wouldn't notice losing us as a customer, while the ERP firm would.
It isn't some conspiracy to keep you from fixing your car. That conspiracy is their engineering management doesn't want the cars to be fixable at all, and they want any unfortunate mechanic who has to deal with the abomination to properly suffer. --insert stackoverflow post about using regex for html--