Social mores dictate that it should be the men who pursue women. Alice's aggressive pursuit of Bob, even if he does like her otherwise, is damaging his social standing and making life for him and his family difficult.
The way Alice is aggressively pursuing Bob would be treated very differently if it was genderflipped to Alex and Bobbie.
Evan chases after Danielle, much to her dismay.
Violet likes Bob, but even though he's aware of her affection, her shyness and fear of actively pursuing a relationship with him leaves him cold.
Bob is glad that Alice would take the initiative and also likes that someone's interested in him.
Subverted: When Alice starts pursuing him, Bob is thrilled that she's so interested that she's actively coming after him and kick-starting their relationship.
Double Subverted: Though her obvious interest in him excites him at first, Bob soon realizes that her aggressiveness isn't charming so much as it is creepy.
Parodied: Bob has been fawning after Alice. But the moment she shows a hint of returning his affections, he panics and tells her to back off and stop being so pushy.
Zig Zagged: Bob can't decide whether Alice actively pursuing him is good or bad. His reaction to it depends greatly on how he feels about their relationship at the moment.
Averted: Alice's aggressiveness isn't a factor in Bob rejecting or hooking up with her.
Enforced: "Guys are usually put off by aggressive girls, so there's no way Bob would actually want Alice."
Lampshaded: "You're always chasing girls around and you don't score shit yet when one actually wants you, you turn her down?''
Invoked: Alice is afraid Bob will become attracted to her, and so deliberately becomes more assertive so as to be intimidating to him.
Bob wants to date Lola, who isn't interested; knowing that he doesn't like aggressive girls, Lola pretends to be suddenly super-obsessed with dating him, expecting that to drive him away.
Alice asks her friend Hannah for advice. Hannah secretly likes Bob herself, and deliberately leads Alice to think she needs to aggressively pursue him despite knowing he hates that sort of thing.
Defied: Bob reasons that a girl interested in him his a good thing, and accepts Alice's offer.
Discussed: "Maybe we should tell Alice that carrying around a net to capture Bob isn't going to make him like her?"
Alice's entirely public pursuit of Bob — and his equally public rejections of her — damage both their reputations. Alice is treated as if her wanting a relationship with Bob somehow makes her a slut, while other girls who were interested in Bob before decide they don't want to risk being rejected and shunned just for showing interest.
It turns out that the whole reason Alice has been pushing her affection onto Bob is because she has had a string of abusive relationships. Having never been allowed to say "No" before, she struggles with accepting that Bob can reject unwanted advances.