Have they got an outside company providing it or is it for their regular teachers to run?
If school morale is low there may be issues enticing staff to provide these extras free of charge.
Schools have barely anything at the moment. Maybe they are trying to generate funds for elsewhere in the school.
Maybe they are trying to attach value to the sessions as students are not appreciating/using lesson time wisely.
I do revision sessions after school and repeatedly tell students and parents I am there to help - cheaper than a Maths tutor! I have had three regulars since September...
However I refuse to have anyone that has been disruptive to class or does not put in adequate effort in lessons at my after school sessions. They earn the right to attend through their learning behaviour during lessons. It's my time and it's not for making up because they gossiped through a lesson earlier in the week.
Know it will be busy in a couple of weeks before the exams. Many come, chat with their friends and count it as revision so do nothing at home - but that's a whole other issue!
Good luck to you dc - hopefully the school will explain their reasoning.