When your home sitting on the couch/play station ect...there's a girl practicing to take your position in the lineup. Even though my DD's team may not be practicing we will practice on our own.
While I agree in principal with what you are saying if a large portion of the team isn't practicing you are in trouble. Come tournament time you have to field a team so you can't sit everyone that doesn't come to practice.
The truth is they should find a team that shares the same commitment level.
Gunner makes an excellent point. In my experience teams that dont share a similar commitment level do not last long. At 12u we practiced twice a week and it was mandatory with some exceptions. Now at 14u we are practicing three times per week. We have several girls involved in spring sports at school so it is not mandatory but attendance from the others has been very good so far.