Garrett's going into his 5th year option, that isn't accounted for. Then he's getting re-upped. A decision needs made on Njoku too. Vernon, Ogunjobi, and Hunt are free agents. The only DB's under contract are Ward, Greedy, and Redwine. The only LB's under contract and Takitaki and Wilson. Then there are the Baker and Ward contracts looming the year after (Chubb's gone).
That $65m in cap space won't go very far. Giving 20% of it to Williams while also giving up a meaningful pick with all of those other holes has consequences. And that's if the cap goes up as originally projected - given what the 2020 season may be like the cap may go down for the first time in years.