You see elite players hit free agency all the time in the NFL. Teams like the Broncos are able to take advantage and sign those players to bolster already elite teams. Teams on the rise like the Raiders and Jaguars recently are able to sign those players in an attempt to help get a young developing core into the playoffs. By removing the talent from the free agent pool in MFN, no team will be able to do that here. This would completely remove an interesting facet of the game and the opportunity for savvy managers to engineer quick turnarounds for their teams.
With the examples you've mentioned, maybe if the managers had paid more attention to their cap management and the contracts they handed out, they wouldn't have found themselves in such a position. I have never had a problem signing any of my free agents and have built championship teams where my star players never hit free agency until they approach the age of 30.
Perhaps you want to change it to gain an advantage on YOUR end - the ability to retain all of your best players despite screwing up your financial situation. Giving teams more time and cap space to re-sign players simply allows managers to put even less effort into roster management to keep stacked teams stacked.
If you put in the necessary effort to recruit star players you should put the necessary effort into ensuring that you can keep them too. If teams are given more cap space, you'll find that there are no star players to recruit at all in free agency.