I have no idea how long they will able to do that and if they actually lose a lot of money or if it works for them.
I suspect that won't last, mostly a question of educating the potential buyers about the alternatives. You can get a brand new Rigol for about $350, which means that for most people the real value of a decades old 'low' BW analog scope is far below this figure. However, this does require beginners know about the other options.
As for more recent medium cost models, then I don't understand what is going on. When the resellers ask more for a 10+ year old DSO than a comparable new model cost, then something is up. Yet I would assume potential buyers for these models would be sufficiently well educated to know about their options.
For instance I have been keeping an eye out for a better scope for my home lab for a bit, just to consider my options. While I could occasionally use 4-500MHz bandwidth, maybe from an old scope, I also have to consider that the list price of a brand new 200MHz DSOX-3024A is about $4700. This comes with a 5 year warranty, says 'Agilent' on the front and is VAT/tax deductible. That makes paying several thousand for a 10 year old dual channel instrument, perhaps even without a proper VAT receipt, a complete no-go.