You have ‘just friends' cuddles with Princess Twilight to keep you warm on a cold winter night. However, the ‘just friends’ part soon becomes rather difficult.
Seriously, they are. This is by far the most important issue, if they made their asses fatter it would improve viewership. If they made the ponies thicc prudes would complain, which would only draw in even more viewers. Twilight Sparkle, the protagonist of the series has a fat ass, and her teacher Princess Celestia, who's ass is even fatter.
The main reason is uncanny valley. When something looks human but not quite. A perfect example would be a robot trying to mimic being human, it looks unsettling. It's somewhat insulting towards the ponies, you have Twilight Sparkle there a beautiful unicorn and you can't embrace her just because she's not fully in human shape, even though she has all the qualifications to be a sapient-minded
I am sorry about this blog, but anime as in japanese cartoons made in japan are under attack by western moral puritans, because it doesn't adhere to their moral standards. This strikes me as a very imperialistic mindset, not everyone has to adhere to our values.