I think the main reason is that it caters for all tastes
the things which would be liked by trp audiense:
Kokila modi type saas
grand melodramatic families
wedding dramas and celebrations, functions...
religious stuff
a few irritating characters
and more... (cant recall right now)
the things which would be liked by online audiense:
two hot brothers and cool nanu
goodlooking lead pair
the female lead is not a bechari type character
the male lead is the Total Package
good music
positive and modern atmosfer
a different approach to the concept of arranged marriage
even though it has kokila but her being modern kinda makes her less annoying
and more... (cant count all right now)