With maybe totally different requirements on the G forces and vibrations that the equipment and people inside a Starship must withstand compared to flying. Not necessarily all the existing equipment can survive a Starship launch and not necessarily all military personnel can fly in a rocket. Of course they can select the personnel, like they do select paratroopers. Fixing the equipment or developing new one might be costly.
Thankfully, military stuff that is field deployed typically already has insane shock and vibration requirements. We build military stuff at our facility and it all has to go through lots of shock, vibration, and temperature testing. The military really wants to be sure things don't fail on the battlefield (which could also be aptly called "the-shock-and-vibration-field")
Just want to add that a lot of military equipment is already designed to be airdropped in addition to any other expected battlefield stresses, so they’re probably some of the best candidates for rocket transport in existence.
There's some work needed to have the launch flexibility though.
Ie lead time to launch, multiple launch locations.
In comparison, simplified, if you have a bunch of things you need to send somewhere, you can go to the nearest airstrip and call a bunch of C5:s from somewhere a couple of hours away.
That could actually probably be worse as the orbital path would not likely go near the wanted landing site, potentially in days. And anyway how do you know in advance what you are going to need (if it's not a nuke)?
Instead, with a near-future rocket, you could have some sort of assortment of "most likely stuff needed" stored near a launch site and be ready to pack and launch in an hour.
It's the C5 Galaxy, but with only a couple of hours needed to deploy into any theater in the world.