That's not the only explanation.
A very real possibility is Jody has instructed NO that he cannot increase the team's salary any further. That would limit his ability to sign 10-day contracts & gives a justifiable reason why the team has kept the open roster spot(s) despite the number of injuries.
Remember, with Nurk, Collins, Hood, & Skal all being out - Portland could've temporarily signed a 15th & 16th player to the active roster. Instead they've kept it at 14 players - which leaves Portland with only 9-10 healthy players every game.