It's not that I don't want them to make a profit - they should price the car and the service plan at a level where they expect to make a profit obviously. But by having at least the option to buy the lifetime coverage it means they have to show you the real expected cost, and then you can make a decision.
Unless they're unified, it doesn't make sense. eg. a mechanic can't easily offer a lifetime service plan, because they don't know the state of the car that you want covered, they would have to do an extensive checkup on the car before and it would be hard to price against expected cost. Separately, it makes no sense to buy a 3rd party extended warranty when it's not the mechanic offering it, because the warranty company is only interested in you not getting reimbursed, and the mechanic hates to deal with the warranty company.
Of course this doesn't exist. The reason is that it removes *three* different ways for them to fuck you over and make not just a fair profit, but an exploitative profit. 1. used car sellers of course do want to sell you lemons at inflated prices, and this stops them, 2. mechanics of course want to overcharge you and do unnecessary work, and this stops them, and 3. warranty companies want to charge you a lot and then not actually pay out claims due to some technicality or exclusion.
But amazingly it looks like Hartech in the UK actually offers the comprehensive sale-to-service plan.