Though its pretty old post but a very interesting question.
I have had the same experience, with two seperate females. Everytime I started working out and focussed on grooming/clothing..they will always say the same lines.
There are materials out there on sexual market value for both sexes. I imagine these females feel if you get shredded your already high SMV will further skyrocket.The bigger insecurity they have is that because of your
Dick size you must have a reputation among girls you dated in past, or sex partners and you/they might be in touch with you. The risk of one/more of these females chatting/meeting you will be way higher as long as you give the alfa male vibe.
With a dad body..your perceived SMV in these two females eyes..and females in general(who hadnot sex with you) will be lower than if you are shredded and muscular.
Thats what they are trying