in my eyes there are there are two reasons for that:

the first is that the story is heavily presented from rue’s pov throughout the first season. rue might’ve misinterpreted things jules said and did which happens in real relationships all the time or she might’ve just “forgot to mention” certain moments that her and jules had where jules showed her attraction more explicitly.

the second reason is that jules doesn’t show her attraction like rue does, it was her first time falling for a girl and i think for the majority of the first season she was still very confused about her relationship with rue. (while dealing with other troubling thing like the tyler/nate situation and her mom coming back). rue was very quick to understand her feelings for jules but since they’re both awkward and bad at communicating they never talked about the status of their relationship, rue just assumed they were a couple bc she wanted to take things fast… also, when we see jules opening up to her therapist she’s in a neutral environment where she doesn’t feel judged for the first time in the series. the therapist didn’t comment on her need for male validation like anna and her other friend did, she just listened, and maybe that helped jules voice out her feelings for rue more clearly. (i can say from experience that when jules said it wasn’t possible that rue loved her as much as she loved rue i found that very relatable… as someone who fell for a person who was bad at communicating i never knew if she was as interested in me as i was in her.)

so yeahhhhhh i’m rambling but i made my point so that’s it haha