So, without going into detail on my own working relationship or contracts with WotC--because even if it weren't grotesquely inappropriate, it's nobody's damn business--I will say this:
If WotC were offering such a contract, it would be the exact
opposite of making a freelancer's life harder. Given how much better WotC pays than anyone else in the industry, the promise of a reasonable amount of steady work would
more than make up for the inability to go to other companies. Heck, I'd kill any one of you for such an opportunity, if I had to.