Muscular men plays a big role in action anime and not in all genres but an exception can be seen sometimes in comedy genre too. Shojo, martial artis, sci fi doesn't necessarily involves a muscular men as it is not need to show martial arts in this genre.
This trend of masculinity in shonen anime comes from 80s hollywood movies and this trend continued to grow. It can be seen in Jojo's Bizarre Adventure. Dragon Ball Z other popular anime displayed the muscular characters. Nowadays every popular anime follows these things.
Do Japanese Woman find Muscular men more attractive?
No, on the other hand they like slim trim boys. Females like men who have slim figure. This is also the case with of the East asian countries too. The qualities include pale face, slender, hairless bodies these type which are not right in the western world.
They like these kind of feminine looking men also due to the fact that they find them harmless. There is also Confucianism. Confusian ideal of men is the kind of men which are respectful towards their parents and are genius or scholar. Therefore being macho is not very good in Japan. Macho kind of figures in Jaoan usually those people have which are either criminals, professional wrestlers and the men whom they want to settle with.
For exmaple yukio was mocked just because he was muscular and not have feminine features. But this is not the case with all of Japanese women some women thinks David Beckham is very attractive to them and they are crazy about them. So, it can also be a matter of preference and who they pick.
Why do anime characters have realistic bodies?
It cant be said all the time as there are some times when anime characters don't have realistic bodies. For example, sometimes the mouth of a character is wide open which is totally unrealistic and sometimes the eyes of the characters are big compared to smaller eyes which seems realistic.
On the other hand, some have weird proportions as they are fat on the upper side as well as some are extremely thin. But they have more realistic features than any normal American cartoons. In the western or American characters they are extremely cartoonish and not a single inch of realistic features are present.
The things like big eye balls or sometimes dropping their jaws are a way of expression through which they express their emotions generally. Which may seem odd to some people. We can also say that characters have semi realistic features based in their appearance like eye balls, jawline or mouth.
We can also find out anime lookalikes in the real life too as they resemble a normal person. Some can argue that eye balls of some character are bigger than most real people out there too. This thing is not humanly possible these are all the reasons given by some people. The lips are just a line or a nose is just a line. It is basically a drawing honestly saying.
It looks like realistic portray of a person. The fact cannot be denied that they look more realistic than normal cartoons. They have more specific features. Some times the art style is drawn according to a real person.
They may be drawn to look according to K pop or J pop. Sometimes these are also the case. We can see various comparisons of Anime characters and K pop or singers or other famous people sometimes.