I think CBB is still all about the coaches. Yes, you need the players, and the portal allows you quick access to players, but it takes a good coach to find the right players and mesh them into a winning team.
The SEC has been helping schools hire good coaches, as well as steering them away from problem coaches.
In 2016, the SEC got 3 schools into the NCAA tournament. Sankey then hired former Big East Commissioner Mike Tranghese as a basketball consultant, who then hired Dan Leibovitz as SEC basketball czar.
Together, they have built this monster. They have worked with the schools and tweaked scheduling with an eye toward maximizing RPI. Bigger than that, though, they have been very hands on with every coaching vacancy over the last 7 years.
There's been a lot of money spent on facilities in the league over the last several years as well.