Cas have made a big gamble on getting funding for their stadium, which if it comes off will give them a strong revenue stream going forward. If it doesn't come off they will either have to play elsewhere, and pay rent, or drop out of SL - that has been made clear by the RFL.
Wakey have no chance of buying their own new stadium, but have a business plan which means they can afford to be anchor tenants in a community stadium and still play in SL - their revenue stream wouldn't be as strong, but after maintenance/staffing costs of a stadium might not be too far away from Cas' potential.
The big difference is that if Wakey play at GH then Cas get yet more revenue, whereas if Cas play at NM the COMMUNITY benefits from the extra revenue to the stadium.
RW has now made it difficult for Cas to swallow their pride in the event of GH failure and play at NM (IF it is built!) - it's a very high risk strategy, and if I were a Cas fan I wouldn't be too happy with my clubs future being gambled with like this.