It was all about the money. He was betting the cap would increase with the new tv deal. He wanted a shorter contract to come back to the table for more money.
Yes, sorta.
It was also about them not extending him earlier.
He would have taken a 6 year deal in 2018(2 of rookie deal bases plus 4 extended), a 5 year deal in 2019 or a 4 deal in 2020.
Dak could very well play hard ball and say I'll only take a 3 year deal in 2021.
He can do this because QBs are too big to fail. The salary for franchise QBs always goes up.
If Dak hits true unrestricted free agency he will be the highest paid QB in football by AAV next year.
NFL teams have plenty of mechanisms to lower year 1 cap hits and plenty to create cap room.