Because muscles are often a sign of strength, and we're hard-coded to seek out mates who can protect our offspring. Just like guys are built to like certain types of girls. Of course there's always exceptions, I'm just generalizin' here.
Because I like to feel safe when I'm in the arms of the man I love. TO much muscle is a turn off, but a good tone is sexy(: Its like asking why do guys like skinny women? because they have a nicer body shape (: SO guys with muscle show females that they arn't lazy and can handle there own if they needed to(: jmo though.
It shows that they take care of themselves. Also generally means they have pretty good stamina.
i love guys who are not too muscley but are toned at the same time. I'm attracted to it because its just one of those manly things I love. I'm really attracted to men with really manly features. I don't really like guys that wear stuff that's really feminine like really tight jeans.