It's my understanding that Big Ten baseball was fairly competitive nationally until about the mid-80s. I read somewhere that the NCAA moved the start date earlier to Feb 1--I think sometime in the 80s or 90s, but I don't remember. That's when southern teams really got a stranglehold on the sport.
Meanwhile, baseball became almost an afterthought in the B1G for about 20 years. There was a period in the early 2000s when it was regularly a one-bid league.
Then B1G schools started reinvesting with Big Ten Network money and tv coverage improved in the 2010s. I seem to recall that almost every B1G school has either renovated its baseball park or built a new one within the past 15 years. I believe there was a season when the B1G got 4 or 5 NCAA bids within the last half decade or so.