The rules do make sense (kind of)
Gov want to reduce a spread of a virus to protect NHS in order for them to be in a position to carry out vital services and not be overrun by covid.
Gov know to reduce the spread people have to minimise mixing especially when they are at higher risk of being exposed.
Gov know it is not possible to eliminate all mixing, and for essential services and economy to function they have to find a balance between resuming as normal, and maintaining restrictions.
If all NHS staff isolated, we would have no services, people would die as a result.
If people who worked in food industry isolated, we could experience shortages.
If children have to isolate from school, it's annoying, effects education, but no one dies and the economy doesnt take as big of a hit.
There has to be lines drawn somewhere, and unfortunately means some people will draw the short straw.
Just like when people complained we weren't allowed to mix in doors, but could mix in pubs. Pubs need to function to provide jobs and aid the economy, mixing at home benefits no one but the individual. Therefore, when making decisions on finding a balance between keeping economy alive, allowing some freedom while reducing the spread of a virus, then obviously the mixing at home is whats gotta give. Which is similar to the current situation of whom the isolation rules does and doesn't apply to.
Its unfair, but logically it does make sense.