In my defense I tend to headcanon that they do the current US federal troop practice of putting soldiers families in their home bases, and then troops will rotate out into a deployment and others will rotate back in without necessarily dissolving or relocating the unit that they are a part of. In other words I tend to assume that is generally happening on a slow burn, since that tends to be necessary anyways to give people a break.
I would agree that this rationalisation work to a certain degree. It completely depend on the situation and why a rebellion occur. A democratic nations soldiers being stationed in an otherwise democratic area that simply want independence might very well gain the sympathy of the soldiers stationed there and they will basically react with apathy or even go over to the other side if they have families there.
The soldiers might view the local population as otherwise friendly and see how corrupt their own government is in comparison in other circumstances. Or simply they don't want to risk their life for a cause they don't believe in.
There can be many scenarios where no matter what you do it will not be enough as it is mainly a war of ideologies and not weapons.
The war in Vietnam that started long before even WW2 was mainly a war of ideologies too... it was not directly won with weapons. As one example...
From a role-play perspective you can rationalise it either way.
If Steve want to incorporate some details you could perhaps choose the type of forces in on a planet. Are they local militia, regulars or galactic troops. How are they interacting with the locals, do they interfere with local government, policing the streets or outright suppressing the populations using harsh means. Whatever you decide to do it would then have consequence on what can happen on that planet.
Having the force being local regular soldiers means they cost normal maintenance while having galactic troops would raise the maintenance on the troops but also make them more loyal to the central government.
It then also would be important which planet is the empires capital as galactic troops there should cost normal maintenance.
Then what happens on a planet should then depend on the galactic states government for and the rebellious planets government form. Is it more of a peaceful independence movement or an outright rebellion that even might lead to a big civil war including multiple colonies and systems defecting to the new faction.
There probably are as many reason to rebellion and civil war as they are rebellion and civil wars...