Policy change
If you get swindled on Steam, Valve doesn’t want you to come crying to it anymore. Used to be if you were tricked out of an item in a Steam trade, Valve would restore it, but an update in the Steam Trading Q&A ends that.
“We sympathize with people who fall victim to scams, but we provide enough information on our website and within our trading system to help users make good trading decisions.
“All trade scams can be avoided.”
The other reason given was, “Our community assigns an item a value that is at least partially determined by that item’s scarcity. If more copies of the item are added to the economy through inventory rollbacks, the value of every other instance of that item would be reduced.”
Likely though it was just a pain in the ass to root through requests.