Simple supply and demand, surely?
There is an over supply of willing low hours instructors, willing to accept whatever they can get just to get some hours in their book.
There is a shortage in supply of students, as prices have only gone up and up making having a PPL as a leisure activity harder to achieve.
Therefore instructors have to accept what they can get, and the schools have the power as there is a queue of people who would take any instructing job.
For things to change, there would have to either be a shortage of instructors, and I don't see that happening soon. Even an excess of students probably wouldn't turn it around, as the weather would still cut a lot of the work out.