Well, Ask MiLB.com got that question along with a bunch of others that might be worth checking out if you are curious.
So....Just because there are! Okay!Why are doubleheaders played for seven innings? --Christine T.According to Rule 4.10 (a) in the Official Rules Book, Minor Leagues have the option to adopt a policy where all doubleheaders consist of two, seven-inning games. It's most likely done to get the games completed in a timely manner, considering it's a good value for fans and also accommodates the bus travel plans of many teams.