Remote Controlled land and water units would also work.
There are multiple reasons why it's the future.
1. Cheap to make
2. Can be smaller since they don't have to have space for humans to sit in them, which might increase ability to carry things, longer range etc.
3. Because humans don't have to be inside of them they can also go a higher speeds, maneuver faster without human body limitations
4. If a drone goes down, the drone pilot can man another one. All that training and knowledge is retained. Human operated vehicles have a high probability of losing their occupants.
5. If 5,000 drones get destroyed, it's lost money. If 5,000 military personnel gets killed it appears much worse in terms of optics, value of life etc.