I think we're missing some information here when talking about Missouri not having spring ball and Texas having it. Here is the wording from Texas' equivalent to MSHSAA (UIL):
Spring Training. There shall be no school football practice or training for a contestant or team, and no football equipment issued after the close of the regular season schedule, except as incidental to the football championship playoffs and, in Conferences 5A and 6A only, 18 spring training practice days which may be conducted in a period of 30 consecutive calendar days. Exception: Conference 5A and 6A schools may choose not to conduct the 18 days of spring training, replacing said training the next school year by following the workout days as specified for Conferences 4A, 3A, 2A and 1A.
Summer Practice. Any specific grouping of high school athletes during the summer months for the purpose of conditioning and/or organized athletic (football) instruction is prohibited and is a violation.
It seems to me that we actually have more allowable contact days; we just do it in the summer rather than the spring. Also, it seems that they only allow the 2 biggest classes to do spring ball.