Tbh the cvs never showed why and how Sahil fell in love with Swara or got obsessed over her. I mean one day he was being a prick to her and the very next day he was gonna propose or whatever (the ring he bought with himself to Badi). As for Sanskaar, we know what attacted him to Swara; her selflessness, loving and caring nature, etc.
Anuj has previously said that he doesn't know anything about the show prior to his entry, so he obviously doesn't know what Swara's character is really like.
It's stupid as an actor to not study the background of the show or about its character. I am pretty sure if Varun was asked why Sanskaar is crazy about Swara then he could possibly list a number of things b/c SwaSan's lovestory has been properly developed over time.
It's ignorant on the part of the creatives to not justify a character's action and it's more ignorant on the part of an actor to not know his character's details.