The constraints are real. Again, it's a two-step process:
1. You have to have 60 credits from Wake to graduate from Wake. This makes it really tough if you are transferring with 60-120 credits. Could you sell a kid with ~68 credits to sacrifice some / take extra classes to catch up? Maybe. However, even if a kid is willing to sacrifice credits, if they fall too far behind academically they can be ruled ineligible by the NCAA.
2. Each department head decides what credits get accepted to their major by fiat. This is where the weirdness comes in and one players' credits get accepted from, say, ULM (Kevin Pointer), and another's might get rejected from, say, Illinois (Casey Washington). It's different department heads making each decision.
Comparing the coaches, I'd be surprised if you find any transfers from Forbes, Walter, or Clawson that don't meet step 1. It'd have to be a specific scenario, likely a player with credits in the 60-70 range and willing to catch up in the offseason. It'd take a good sales job, too. For players under step 2, it likely comes down to which academic programs the players are in and our experience with getting transfers in with their credits accepted. I'm sure the coaches know which programs are permissive and which are restrictive to transfers.
Clawson also might be more gun-shy than the others. He had the experience with C. Washington where the kid was literally in classes at Wake for 2 weeks before learning that his credits from Illinois wouldn't be accepted.