I agree, at least how their relationship has been written thus far, there hasn't been enough ground lain for the choice, for Lena to
like him (in the context of an EvaKiss VN).
Unlike most games, the most important feature of EK's writing, I think, is not leaving the emotional reasoning behind the MC's actions for your imagination. Instead your choices are used to develop the MC's feelings, then those are codified in clear monologues and conversations. There's some exceptions when we get radically aberrant choices, usually for the over the top routes and the superslut h-scenes with little LI development. (The polar opposite, where contradicting the personal development is necessary for the eventful plot, is Village Slut...)
I
can very much see a way to make the Stan route reasonable if he's developed as the opposite of Axel AND Ian either does not pursue her or turns up the toxicity, he can be a safe haven for a hurt Lena who, based on our choices, has lost interest in "Chads" or finds them threatening. He'd be similar to what Ashley was for Good Jess (or like
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?). Of course a manipulative Lena also can have a Stan route, either as a training experiment for her camgirl or sugar baby routes (but the latter is wobbly enough as it is and she porbably should drop Stan once she hooks the big fish).