This article in the Statesman illustrates a pitfall of Charter Schools, they're still government supported schools:

Some parents at Hidden Springs Charter School who say their children are unfairly treated by the school's admission policy are demanding their students be allowed to attend the school.

The school's policy for establishing a waiting list for students who don't get into the school is a "violation of law" wrote Ken Mallea, a Meridian attorney representing the parents, in a letter to Monica Cockerille, School Board chairwoman.

As such they still face government regulations and have to comply with a lot of the same requirements public schools do. This may also be because Idaho's charter law is very restrictive per the wishes of the State Education Association. Only 6 new charter schools per year are allowed in the whole state, so its not like these parents can just go and start their own. Schools that are good and successful are going to have a backlog, but the Education Association has a benefit in avoiding the creation of new charters because Charter School Teachers are not part of the IEA or their collective bargaining agreement.