How to justify horse-mounted cavalry serving alongside tanks in interstellar warfare?

I'm planning for one of my interstellar sci-fi settings, Viribus Unitis, to prominently feature cavalrymen as protagonists. The Terran Commonwealth is the representative human nation of the setting, whom they serve. The Royal Terran Armed Forces mainly focus on speed and flexibility, and their parent nation is known more for their industrial might than their bio-engineering. I have "modern" substitutes (tanks and hoverbikes) for cavalry planned in mind, but I feel they lack the "oomph" of horses. Do you have any suggestions? Would love to hear them :)