You're missing a very important factor: Minor league baseball teams have often (not always) paid the radio station for coverage, instead of the other way around. Moving to streaming eliminates an expense and potentially replaces it with revenue.The teams sometimes make decisions to pull their games off of radio. The Tacoma minor league team used to be on the radio, and now it's all broadcast via app.
Years ago, I board-oped eighty-some minor league baseball games. The club paid us around $100 per game, we refused to air games on weekday afternoons (day games were usually rainout-related twin bills).