Use cases where the release valves of the web UX and normal mobile printing don't work, even ignoring the obvious benefit of Universal Print being made truly universal:
MDM systems like InTune support and often are used for blocking features like printing from the work side of an Android device. I can't print work docs anywhere from my phone.
Similarly, it's not at all uncommon for printers at the office to be unavailable to mobile devices, either because their approach to zero trust network design methodologies lead them to block all lateral communication between endpoints or because the less trusted, often much less intrusively managed mobile devices wind up on a separate WiFi network or VLAN from conventional enterprise devices like laptops and printers.
In either scenario, the benefit to the enterprise complex enough to want to use Universal Print is clear and considerable if Microsoft either makes these services available directly from InTune for iOS and Android [and/or] presents a unified user experience for mobile by adding the same basic Print button found in the web UX to their mobile apps.