Tory Education Policy

You'll have to forgive me here, no, I'm not playing dumb, I really don't understand the logic here.

Hundreds of failing schools will be removed from local authority control in some of the worst areas of deprivation under radical plans to be unveiled today by the Conservatives.
...

Legislation will be included in the first Queen's Speech to remove up to 640 of the worst secondary schools in England from town hall control in a move that will be fiercely opposed by Labour. Most of the schools are in its northern and metropolitan heartlands.

Control of the schools would be switched to city academies, charitable trusts, and parent co-operatives in the biggest shake-up in secondary education since the introduction of league tables in 1988.

Now, I agree, getting schools out of the grip of the centralised bureaucracy and into the hands of those who actually use them is a good idea.

But the logic here is that such authority control makes the schools worse than they need to be, that they will be better when more responsive to users needs.

And again, I agree this will be true.

But why does the logic only apply to 640 schools: why doesn't it apply to all?

Why aren't we simply abolishing all local authority control of schools? Why aren't we setting them all free?