More like the capability of the owner IMO. A lot of cars aren't taken care of, and it's a daunting task to replace everything that's been neglected since new, then it is to replace a component here or there.
It's hard to justify installing a transmission in something with an engine that leaks, an exhaust that is rotted off, rust/dents in every body panel, and the accumulation of a 2 pack a day habit residing in the interior. Whereas I wouldn't bat an eye on doing that to the same car that's immaculate.
For instance, I just had that exact scenario in the shop. One was a 25 year old camry, and the other was a 10 year old altima. One was taken care of, ran well, and was in immaculate shape. The other was on 4 bald tires, brake wear indicators scraping, and the floor pans and exhaust was rusted out. Guess which was which? If you guessed the camry got the trans, you would be right.