Because they're sad, sad people with nothing better to do with their lives except hate on people who are better than them.
Ally is probably one of the kindest, most sincere people in the music industry right now, she's a great singer, and she's very pretty despite having an untraditional body type in terms of celebrities, but people choose to ignore all that and hate on her because she's short, not a great dancer and she's "extra" (which is apparently just becoming synonymous on here with being a nice person).
Because she's short, kinda chubby and has a very unique body shape & doesn't have as much "sex appeal" as the others. I feel so bad for her bc she's so talented and probably has one of the best personalities in the group but people are stuck on how she looks.
This is the same way people treated Michelle in DC but at the end of the day, they were both in two successful girl groups and y'all posted up on the internet judging lmao
She's not chubby Cuz because she's not Ariana weight as a short woman doesn't make her chubby.