Thunderbolt encapsulates the DisplayPort data in Thunderbolt packets, so both endpoints of the link need to be full-featured Thunderbolt devices.
When there is a better way, why would you spend money and effort supporting the old outdated way?
It may not sound like a big deal, but I have an LG monitor that uses a remote for input switching and volume controls, and a BenQ monitor that uses buttons, and both provide a noticeably jankier experience.
The Studio Display provides a very clean user experience when paired with a Mac. You plug it in, it turns on, and all other functions (volume, brightness, colors, camera, etc) are controlled via MacOS. Personally I'm happy for Apple to optimize for that experience, at the cost of not working with non-Apple devices.
If you want old connectors , why not put a scusi port on that thing!