I said it before in the Bucs thread, but Brady doesn't care about roster/team building. He only cares about winning titles. In fact, I guarantee you that Brady knew about AB's CTE/mental issues before recruiting him. He doesn't care if AB gets hit or compromises his health as long as AB helps him win rings. Same deal with Gronk, who Brady knew had nearly 20 concussions and 10 surgeries over the years.
Bill, on the other hand, could simply not afford to bring the kind of talent Brady was begging for via free agency/trade.