They want to keep payroll down and delay starting as many service time clocks as they can. You need cheap arms to eat innings to do that.
Holt and company aren't Rumpelstiltskin, they are not capable of weaving straw into gold. Frankly they have more important things to be working on.
Not sure what they see with Waddell. Only scouting report I can find on the guy is from like three years ago and calls him a "four-pitch pitchability lefty who has trouble commanding his pitches." His professional walk rate is like 5-something.