New bubbles versus key worker children

[NCTDN]

I don't get the new guidance. From June 1st we need to be in bubbles of no more than 15. Staff not to mix between bubbles and no rotas. Yet until then (so still another week) we have had key worker children in school and staff covering on a rota basis. There will be staggered start and end times yet so far children come in and leave at the same time.
Why the sudden change?

Because there will be a lot more children? (potentially all of reception, year 1 and year 6)

With keyworker children we have had anywhere between 2 and 12in school and were childcare, next week we will have 90 and are a school!

We will probably be at our maximum number just with key worker children, yet will have to have a different set up than what we've had so far.