Rs. 1099 Super+ plan provides ad free experience with Full HD streaming, Dolby Atmos Audio and supports simultaneous watching on 4 devices .
Premium plan which r talking about provides 4K streaming and ads r aired in it so that Disney+Hotstar is able generate additional revenue required to help provide additional features.
There is a balance which needs to maintained for investments and revenue, ads help provide premium features in affordable subscription plans to customers rather than keeping than charging more for it.
There r fewer people who opt for premium plans hence ads serve as key source of revenue , they can even provide Ad Free premium plan for Rs. 2000 but again there will be minute number of people opting for it. You need to understand why companies adopt a particular strategy for different plans or even for TV Channels what kind of contribution/role subscription and ad revenue play in channels belonging to different genres or types