the hours for the school day are set by the state, and esp. in districts where kids are bussed to parochial school, the bus determines the schedule, so there is usually not enough time for daily Mass. by the way, the time for religious instruction does not count for the academic hours required by the state, so usually Catholic school begins earlier and/or ends later. Many Catholic schools are not located on a campus with a church anymore, but are independent, like my grandchildren’s school, so daily Mass is an option if parents want to bring them early at their nearest parish, but not for the whole school population.
Our parish school starts at 8, and parents are free to bring their children to 7 am Mass, but few or none do so. There is an 8:15 Mass on Friday am for schoolchildren and parents, but folks on this forum would hate it since it uses the revised children’s lectionary, children form the choir, do the readings etc. Each class takes turns for these roles and it is a learning experience, so these kids really do know and understand the Mass, the Eucharist, the Real Presence etc.
Catholic schools in many districts, esp. in urban areas, have extended day programs and open early for govt. funded breakfast to be distributed to those who qualifiy, another chunk of time taken up.
Also, many schools dropped daily Mass since too many parents think it is a substitute for Sunday Mass, and administrators are trying to drive home the importance of Sunday Mass for the families. Sad but true. There is also the whole issue of REQUIRED Mass attendance, as opposed to teaching the children the importance, centrality and reality of the Mass so they attend because they want to (and get their parents to attend) rather than because they hafta.