My understanding is the key purpose of the policy was to tax private school fees and use the revenue to fund better education in state schools. It turned out it would take years to enact the changes required to charity law whereas it is much quicker to enact changes to taxation in the parliamentary process, therefore getting access to the funds soon after forming a government.
This seems an eminently sensible and pragmatic approach to me, and gives the sector plenty of advance warning to prepare.
I imagine the vast majority of voters, who do not pay private school fees, would not be bothered which mechanism is used to raise the funds and improve state provision of education.
What surprises me is the opposition on here to a policy that creates a clear difference between the Labour and Conservative parties and promotes social justice. I find it quite bizarre, unless it turns out they attended private school, or send their children to one and don't want to see the cost of providing them a lifelong advantage go up.