Its a choice of Customers, STB might be for new & those customer who wants OTT/Streaming & DTH in one platform & Dongle for who wants to take it additional. (Want to change its HDMI source in Tvfor watching OTT & Streaming Services )
How is it Jio effect when Tata Sky isn't offering internet service to run binge device? This is only worth it if the customer has a stable internet connection with unlimited data. Otherwise no use of these OTT services. Tata Sky broadband is also barely available in few places.