Then those schools should be under the same rules as public schools and under the same school boards as public schools.It would be wise to do that, but that doesn't help anyone's kid now.
That is also riddled with political pitfalls in our current education system.
One example: research says that the most impactful school-based factor in regard to student outcomes is the teacher. It makes sense to invest in teachers. The best way to help teachers improve is to provide them 1:1 non evaluative coaching (3rd party preferred), more effective than workshops or the occasional observation. However, unions often bar teachers from receiving coaching either for fear it will be used evaluatively or because it's not in their contract.
Who loses? Students. That issue and many like it aren't going to be solved quickly and you can't make a case to parents that their kid should suffer while we wait for it to be resolved.
The quick answer? Give parents a choice where their money is spent, and let the schools figure out their internal issues on their own time.