I think they perhaps also take the view that if they did the PDI they would find and have to repair more defects, whereas leaving it to the buyer to spot and report faults mean there will be fewer. Some buyers won't notice/can't be bothered.
There's certainly an element of can't be bothered. There's still a problem with the window alignment on the driver's side door of mine, with a seal bulging out by about 10mm and a lot of wind noise, but I've already wasted too much time driving to the Bristol SC and back getting things fixed (including this issue) so I'm going to try and sort it myself (and add some sound deadening inside the doors whilst I'm at it).
The car's only redeeming feature is really the performance, as the combination of the hassle of receiving a car with defects, the hassle of getting them fixed (the SC is over 2 hours drive away) and the ongoing uncertainty as to what's going to stop working, need a reboot, or whatever when there's a software update, has very definitely taken the edge off the whole ownership experience.
Of all the cars I've owned, I think the Model 3 has been the most irritating, with significantly more issues than any other new car I've ever bought. If there was a serious competitor, with a similar range and decent performance, then I'm not sure I'd buy another Tesla when the time comes to replace it. The Model Y would be tempting, as we'd like a hatchback, but there would be this niggle in the back of my mind that it might be a similar experience to owning my Model 3.
The car can be great fun, there's nothing quite like it at all, but I can't help feeling that I've paid Tesla for something that's not really a mature product yet. Nothing wrong with that in some respects; I bought a pre-production bit of new tech for the house a few years ago. However, when I bought that the purchase agreement was very explicit about it not being a fully production engineered product, and that part of the deal was that I'd have to expect some issues and help the developers fix them by giving them data. It wasn't until after buying the Model 3 that I realised Tesla ownership was similar, except I'd paid the full price to be a development test driver.