I worked "surplus" for several years. In my opinion, there a few factors at work.
First: the govt doesn't release as much as they used to. It seems like more stuff is controlled; armor carriers and whatnot. Yes some do get surplussed out, but I new saw huge lots of IOTVs go up for auction like I did LBE suspenders (for example)
Secondly, Govt Liquidation keeps the good stuff and has started selling it on their own.
Want Sleep Systems? Well there selling the best ones on their own website. If we wanted a large amount, we had to buy huge lots and separate the beat-to-hell ones from the salable ones. So that sort of bottlenecks supply.
Thirdly, yes, the Internet. Now that people in Italy and brazil have access to us surplus via eBay (or wherever) demand has gone up, with price accordingly.
It kinda seems like demand across the board has skyrocketed. I recall WW2 stuff being everywhere when I was a kid. I think around Saving Private Ryan, people went nuts, M1923 belts and stuff doubled in price.
Just my brief thoughts onthe subject, I could ramble at length but it's best to keep it brief.