Brief Explanation: Better Controller Compatibility than standard Xinput, More flexible control options, better controller experience.
Full reasoning:
Presently the Controller Support in the game uses Xinput controller inputs, which while standard, is inflexible. Steam Input API integration meanwhile allows for full use of the features of various controllers with more than an XBOX controller, such as the Steam Deck’s integrated controller, Dualshock controllers, and Nintendo Controllers featuring Gyroscopes and extra buttons. Usually the reason to not implement Steam Input based controller support would be to keep the controller support consistent across stores, but given the existing reliance on Steamworks APIs Tower Unite already has, this seems an inconsequential drop in the bucket.
Additionally, it would ease the UI development workload by using the Steam Overlay for controller remapping, and allow for pulling controller input glyphs from Steam Input if desired.