If I had to speculate, I would guess that a number of individuals in the Brewers org must have done a huge amount of organizational building legwork in the 2010s (or even prior to that) to get us where we are now.
I wish someone would ask Mark A the question and see what he says. If I had to guess, I bet he would say that it's not something you can do in just a couple of years. It took Doug Melvin 6 years to get the Brewers to the playoffs and I'm pretty sure when Mark A bought the team it was Melvin coaching Mark on how to run baseball ops for quite a while.
When it was time for Doug to retire, at that point Mark knew what he was doing, had the organization running smoothy, and he had figured out that he had to go get an analytically-minded GM to put the last piece of the puzzle together. That's where Stearns came in and I don't think it's a coincidence that our drafting and player development took huge strides around that time.
In retrospect it looks like Stearns brought some critical pieces to our org but maybe he wasn't a "organizational builder" guy which is what the Mets really need. Or, maybe it's only been 3 years and it's going to take the Mets 10+ years to actually turn things around (even with their budgetary advantages). Or, the fan/media pressure is just too strong in NY for anyone to have the patience to make deep changes.