Why can't some fat people try to lost fat?

I have seen lot of them genuinely work and succeed in getting fit.. thus getting healthy and attractive
But lot of them are very insecure about their looks and get pissed and call the people who advice them to lose fat as "Fatphobic"
(Especially if they are fans of ominis gauntđź’€)
Why can't some fat people try to lost fat?
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