I really liked this question so here is my answer ↓
As a lesbian person, I read more BL because I see myself more in male characters, so much so that that's how I found myself in non-binarity. I find male characters attractive, I like to imagine myself in the relationships I read about (this goes for straight couples too), but the attraction comes from the personality and perfection I find in fiction, unreal elements that I could never have in real life or otherwise the way it is told in fiction.
My relationship with male characters is more about identification too (and I don't know where the identification comes from), in addition to my real-life tastes (for example, I'm always attracted to uke while I see myself in seme). Before discovering myself as a lesbian, I thought I was bisexual because of these things, that because I had some "attraction" to male people and characters I could have sexual/romantic attraction to a man, but that's not the case for me. What happened was that I always saw in the male character what I want to be and have (the characteristics and gender expression, not the gender itself), and for me to be attracted to a real man I had a checklist of impossible things that had to be filled in for the attraction to come.
In fact, both with real men and with male characters the attraction that I imagine is unilateral, coming from them, while I am always the side that rejects and feels absolutely nothing. Admiration exists, affection exists and the desire to please and be exists, but not romantic or sexual attraction, you know?
Of course, this is all my experience as a lesbian, there are several others contrary to mine that are just as valid.