Could the same could be said for low end VPS's?
I've been trying to find some figures about average specs but I'm still looking. The majority of machines are probably just used for surfing the net, imagine the old PC some grandma has that she never installed anti virus on... old, useless, but it still ok for email and basic surfing, and since they don't do any banking or need a secure PC they don't care so much about security.
The problem is that there are literally MILLIONS of these machines all over the world. They hash very, very slowly individually, but add them together and you have a massive mining network... for free.
VPS's are not the issue, if you want to use one you'll have to pay for it... free beats that every time.