Hi Roberta, I love your work. I have found a lot more than 5% follow back from FAA even if less than one would hope. FAA attracts a lot of different types of artists so it just stands to reason that a certain % are only semi-active members, semi-active artists, or semi-actively marketing on social media.
I agree you can come across the odd ones who are obviously on social media +/- daily and still don't follow you back or acknowledge when it is fairly clear that they must have seen you supporting them. I rarely give it a second thought and don't even usually bother to unfollow. Why do they behave this way? Probably mostly random. For sure, some artists think if they RT other artwork it garbles or dilutes their message. IMO this is a really shortsighted (but in a way understandable) strategic approach and tends to make a person come off as a grocery manager rather than an artist. Others may feel threatened by you or think they could be at risk of losing sales to you. Given your rather impressive FAA portfolio, this may be the case in your situation. I would hope not, but who knows. Whatcha gonna do? :) It's kind of like office politics 101 or maybe high school. Either way, I doubt if more than 1 in 100 FAAers would fall into this category.
On a separate note, I will say that one of the problems with RTing FAA members is when the "Fine Art America" link, handle or branding is too blatant in the tweet - it is a lot easier to support an individual artist than it is to flog a commercial brand.