Because we prefer getting pissed to educated?
Realistically it is a total nightmare to get schools back to "normal". My daughter is attending because she is year 6, and they have year 5 as well as nursery attending (nursery are in another building). But in normal times there are 900 children on a small and compact site with no room for expansion. There are no expansive playing fields to put portacabins - they would have to go in the playground which is the only open space in the whole school. Then there are logistics such as lunch time. In normal times lunch times have to be hugely staggered to accommodate all the children in the dining hall - if you have to socially distance then the first lunch slot would have to be at 9:30 and the last just before the end of school! And that is primary school - secondary is even worse as the children have to move around classrooms - I cannot see how any kind of social distancing / cleaning could prevent COVID being transmitted from one class to another. The schools problem is structural and nothing is really going to help with this.
So the government have basically given up and are hoping that the situation is OK for schools to resume in September with no social distancing.
Pubs on the other hand can limit their numbers quite easily and put into place social distancing measures based on lower numbers of customers.