Older players just didn't get drafted in the XFL. Clay Harbor, Trent Richardson, a number of others. I think Siliga did get drafted (he's 29 like Gray) but I think they're trying to sell it as an NFL showcase, especially since they're recruiting supplemental draft guys like the West Virginia safety, rather than a weird collection of has beens and never weres like the UFL and AAF. Plus running back is such an interchangeable position, why trot out Jonas Grays when you can roll the dice on young guys who aren't known quantities.
Gray's issue was he was a more or less average talent at a position where there are a hundred guys every year leaving college who are more or less average talents. I feel bad he disappeared after that game, though. Mostly a result of Blount becoming available and injury luck, then the signing of Dion Lewis to a futures contract.