Someone more knowledgeable may be able to chime in.
However, my opinion is that most who are selling this age of vehicle are only doing so due to the vehicle being so mechanically far gone/patched up that it's not reasonable to keep it. Therefore, most examples in the used market may not be reliable examples. It will be rare to find a car that has been maintained 'by the book'.
Now, people who own altos, who are happy and don't want to sell, most likely have kept the car with care. Car prices are insane, so most tend to keep them if they have treated them well and have been reliable. Thus the answer to why they don't want to sell them. It makes no sense to sell your car, then fork out a bunch more money for only somewhat of an upgrade.
So, in short, it will be tough, but if you can find a mint condition gem (rare), then only it may be feasible. Otherwise, like someone else mentioned, keep some money on the side because any used car is most likely going to need some maintenance once purchased.
