The reason not to go back early is that teachers and their unions will not do it and quite rightly in my view. Most have worked over Easter preparing remote learning and have been working hard delivering lessons remotely this term. Furthermore, lots of primary teachers have been in school with children of key workers.
I think the reason for getting primary age pupils in is that parents can then get back to work and get the economy moving. If you have primary age children, working at home is not easy! Teenagers can be left to get on with things more easily (?)