First of all, there are only two lines in the song that mention appealing to men:
So I hardly think that that means the entire song is about appealing to men.
Second of all, it is true that she uses the words “skinny bitches” but may I remind you that she follows it up with “no, I’m just playin’ “. She’s just joking. You must have heard songs with very similar lyrics that didn’t seem like they were joking but she’s turning said words into a joke and lets it be known that she’s not being serious about it.
The overall message is that society has had it implanted in our brains that thin girls are the best girls and fat/chubby girls are inferior and not beautiful, and it’s not true. So many people think that you are not worth dating or not beautiful if you are chubby, and if you have that mindset, if you think that a woman is not beautiful because of her size, then you can just leave her alone because you have messed up priorities.
Furthermore, the song isn’t directed towards girls who are already completely socially acceptable, it’s directed towards girls who have been teased and bullied and pressured to change the way they look because they’re chubby and have more fat than magazine models do. It’s telling them that it’s fine to be like that. Nobody can help the way their body is shaped but if media only portrays one body type as beautiful, everybody who doesn’t have that body type is left feeling left out and thinking that there must be something wrong with them because they’re not skinny.
There is nothing wrong with being skinny, just like there is nothing wrong with being fat, but people who are fat need more reassurance of this because it’s already very obvious that thin is beautiful, and not obvious enough that you still matter very much and you are still beautiful if you don’t look like a magazine model.