To be honest, I think the main reason that good cars are (slowly) becoming more expensive is that old Volvo 700/900 series are getting rarer and many examples are run into the ground by people who just don't care. Also, it's still more profitable to break a car rather than sell it which must be taking a lot of perfectly repairable cars off the road and out of the hands of enthusiasts (not that I blame people for doing this). I bet there are loads still going to the scrappy as well with some owners just seeing them as a junk car.
When you have a look at how many cars are left by various models you can see that these cars are leaving the roads pretty quickly. If the numbers are to believed then there are around half the number of 940s around compared to 5 years ago (and the situation for 740s is even worse). I'm sure the numbers aren't 100% accurate but give a general idea of what is happening.
https://www.howmanyleft.co.uk/family/volvo_940
https://www.howmanyleft.co.uk/family/volvo_740
https://www.howmanyleft.co.uk/family/volvo_240