We need schools and nurseries to reopen so our children can be properly educated and people can get back to work.
Absolutely.
However, schools and nurseries returning to normal FOR FULL EDUCATION requires children to be closely packed in classes of 30+, with their regular teacher fit and well and standing in front of them, and all support staff supporting the most vulnerable, for example those with SEND.
It would also involve older children travelling by public or school transport, also crowded.
There is an obvious conflict between these and limiting the spread of virus, both within the school (not least because when a child becomes ill, for full education the school needs to continue unaffected...) and within the community.
It's about the balance between these needs, because neither 'pure' situation (fully shut or fully open) is without significant risk.