
Aqua:
This is such an interesting discussion, thank you for opening this up. 
I couldn't quote the other post you made, MDL said it's too long, so I'll answer here. That was an interesting answer, it highlights other view points too like you mentioned people wanting to watch something they will never themselves experience. That could go down as a good reason imo.
The point of inserting oneself into a scenario in a show, wondering 'what would I do?' is something I cannot personally relate to since I've never done that, whether I'm reading/writing/watching any movie/show, het/LGBTQ/BL/GL/etc, I watch the people in the show and that's where it stops. So I wonder then, if a lot of het females perhaps like BL for that reason you mentioned, not wanting to have to relate or think too much about what the female character is doing and so watching two men helps then detach it from themselves (even though het/gay relationships varying dynamics and emotional situations and feelings don't differ in anyway other than some physical elements). That could also be a good reason.
You've brought up two reasons here I find very interesting! Thanks!