Men generally are seldom as weight conscious as women.
When I was growing up I was an overweight kid and in the boy's section they had a size called "husky". I can't imagine girls or women being okay with a "Husky" size listed in department stores.
Some stores for men specialize in "Big & Tall" sizes and state so on their signs and marketing materials. They say "Big" not "Plus" size.
Big is often viewed as "strong" when it comes to men.
Pro football players, Heavy Weight Boxers, Sumo Wrestlers, Body Guards/Bouncers...etc Some women claim they feel "safer" with big men. I've known big guys with nicknames like "Tank", "Truck", and "Cannon". I can't imagine many women being fine with that.
If an overweight guy looses a tremendous amount of weight and poses in a pair of swim trunks other men aren't going to accuse him of "fat shaming" them. By the same token there is no "Real men have curves" slogan either to shame small guys. Very few men set out to compete regarding physical appearance.
People Magazine often posts photos of two female celebrities wearing similar outfits with the caption: "Who wore it best?"
Another factor is most men don't spend nearly as much time as most women do on their physical appearance. You practically need a GPS to find the "men's section" in most large department stores.
Aside from clothing, handbags, and accessories there is also cosmetics, shoes, perfumes, hair products, and jewelry primarily geared towards women.
Business people invest in marketing to those who are inclined to buy. I'm not sure if "society" is to blame or if it's simply one of those "gender differences". You look at every awards show on TV and just before the start they have a "Red Carpet" stroll where the women are asked "Who are you wearing tonight?"
Trust me these "pre-show" red carpet strolls aren't designed for the male viewer. It's primarily women that comment on what other women wore, their hairstyle, and jewelry.
"Why does society seem to accept over size men more than women?"
I think (in theory) women accept oversize men more than men accept oversize women.
However if you go to any Wal-Mart, movie theatre, mall, or church you're bound to see many "overweight couples"!