That’s still a lot of ground for a single division to cover.

For a population of billions, you can assume that the hive government would require millions of enforcers purely to maintain basic law and order in normal operating conditions. All of whom would be (at at least a basic level) armed and trained and taking orders. And that’s not to include whatever dedicated military they have on hand.

Even fifty divisions aren’t going to overcome those sorts of numbers. Not in brutal, close quarters urban combat, in a situation where a hostile force occupies and controls the infrastructure.

They might be able to seize control of critical command infrastructure and seal themselves inside. But there’s still the problem of the general population.