Here's just my two cents on what might be the deal with GSP. I think a lot of it is about what he said way back when he first talked about wanting to come back and resume fighting: that he mainly wanted to have fun fights. "Fun fights" are generally those that garner some intrigue, but aren't necessarily a risk to your legacy. Since GSP's legacy exists entirely at 170, I think that could be a reason he avoids the division. He's not looking to resume his status as the top dog at 170, and I don't even think he ever wanted at that 185 either, which is why as soon as he beat Bisping I didn't think there was much of a chance at all that he'd defend that belt. He just wants to take fights he finds interesting but not be beholden to the pressure of being "the guy" at 170 again; he wants the option of winning a fight and not feeling the need to commit to anything following if he doesn't want to (though he did throw MW in flux by winning the title and ditching it haha). And as big a fan of GSP as I am, I do think there's some wariness of the style match up with Woodley on his mind too. He ruled the roost at 170 for a long time and Woodley is a risk that might not be worth it to him when his mindset is in semi-retirement mode.
Not saying I'm for or against that attitude, it's just what I think is probably going on. I personally thought he should've just gone with retiring on top when he won the Hendricks decision (that fight to me was a sign that the division was catching up to and starting to surpass him). I didn't like the whole MW title thing, but when he did beat Bisping I thought that was another perfect time to retire (since I never thought he'd defend). Now there's talk of 155 and I'm kinda just over it. If he just wants fun fights and doesn't want to risk ruining his legacy then fine, but because of his status all talk tends to go toward him holding up other divisions by fighting their champions, and I'm not for that.