Wilbur's academic record showed decent grades. He needed somebody smart, an environment that'd keep his mind active, but it had to be with someone who'd give him real attention and not push him into the background. Hell, his old man did enough of that. He needs somebody who needs someone to take care of.
Once Riddick decided that, it was clear that there were multiple needy candidates. There were two widows who'd applied. Who knew farming was so hazardous? And I'm not sure either of them is that bright, even if the older one does bake a nice fruit pie. (The bribe wasn't going to work, but that didn't stop Riddick from enjoying the change from V-rations.) Another family had lost a son to some exotic disease; his brother was lonely, and they wanted him to have a companion. Nah, Wilbur'd always be second best. He needs to feel wanted.
The potential father who made Riddick take a closer look was the colony's apothecary, a widower. Smart. It's a useful trade for Wilbur to get into when he's older. And I can scope the place out to score more meds for Johns. I think we've got a win-win situation here...