I can't speak for them, though I would imagine the reason, not an excuse, is to make more money? Maybe having these games available is costing them some money.
As I said above, I stopped dealing with this company a long, long time ago.
> Maybe having these games available is costing them some money
Do you mean in the sense of "people are still playing this game instead of buying my new game?". Probably. I would guess this is probably false though -- that people keep buying games for companies they perceive as consumer-friendly.
Or do you mean they lose money by providing customer support? They could just add a warning notice the game is no longer supported, and that you buy it (or play it) at your own risk.
It wouldn't be the first time companies make short-sighted decisions, though.
As I said above, I stopped dealing with this company a long, long time ago.