The thing that's not being factored in is when you're making a 3 for 1 deal the other guy is giving up a good player (very likely the best player in the deal) AND has to drop 2 guys off his current roster to make it work, because of that I'm not surprised these deals were rejected.
The value you show us might be fair but factor in losing a couple roster players obviously isn't worth it.
Basically it's quality > quantity
12-team 5x5 H2H w/4 keepers
OF:C.Gonzalez, Heyward, Burns