Even though Twitter has a pretty UWP app with the dark theme, they hardly updated it. They did not even bother to add simple feature updates like an increase from 180 to 240 characters in a tweet. But they have updated their app with completely a new PWA for RS4 users. PWA, Progressive Web Apps is being considered as the next stage in the software evolution. Companies like Google, Microsoft have been emphasizing on PWA for some time now. Microsoft even encouraging developers to bring PWA to the Microsoft Store.
By using PWA, Twitter no longer needs to work on different apps and service on the different platforms. Literally, one code to rule all platforms. Unlike the web wrappers, these apps can use native OS features like live tiles and notification center on Windows 10. With developers picking up PWA, it would make people use any platform easily and hopefully, Microsoft store will see more official apps.