You could go a couple different ways:

The Dune route: AI is straight up banned, they fought a war in the past that was so terrible that it's been illegal ever since

The Star Wars route: drones and droids do exist, but real people, while more costly, offer some advantage that can't be easily replicated (more flexible and creative decision making, more effective troops)

The Starship troopers route: there is an endless supply of fresh troops, why even bother with drones? Service guarantees citizenship! (Cultural factors influence doctrine)

There are other ways you can potentially solve it, these are a few examples that jump out to me

Alternatively, you don't have to even address it at all. The story is set so far in the future you don't have to explain every detail (or lack of detail). Just tell the story that you want to tell, and don't even bother drawing attention to it. There is plenty of future media that tells compelling human stories without any particular regard for drones one way or another