But it somehow is enough to do that for things like the Mac Pro or the Mac Studio that are clearly niche products compared to the rest of the Mac lineup?
I'm not sure it's fair to compare cars to phones or other tech products. Phones are not very repairable these days, but even if you manage to keep a 15-year-old phone working, the unnecessarily ever-changing protocols, APIs, and standards will render it unusable for most practical purposes. So you're kinda forced to upgrade every now and then. A 15-year-old car though? It takes the same fuel and drives on the same roads as brand-new ones. And spare parts are most certainly still available.
The Mac Pro that famously gets very infrequent updates and is far behind the rest of the line on CPU generarion? I would not be at all surprised if Apple kills it off in the near future.
The comparison to cars is the market. A company makes products it wants to and that it thinks will pay back their investment, and that will be the most profitable choice among the choices of product they could make.
Sorry, you aren’t going to debate your way into Tim Cook choosing a less profitable product to make.
I still blame Apple for considering that 3% of total iPhone sales is a failure. And then launching the iPhone air, as if it will do any better...