Also, the July Monatorium used to a be a month long.
Contracts always end on June 30th, since it is the end of the fiscal year. Therefor teams can start negotiating on July 1st. The audits take about 2 weeks to complete, so teams used to have 2 weeks of negotiating time where they knew the exact cap.
Due to the lack of necessesity of knowing the exact number, teams pushed for the negotiating period to be shorter so they could get a quicker jump on the off season.