Body Weight

Please nobody take this as offensive, I'm honestly just wondering. But when bigger girls ask if they should lose weight, instead of being like "you're perfect the way you are!" Why don't women be supportive about the loss of weight? For example "You look beautiful, but a little weight loss would benefit you and probably help you lead a healthier life & etc. Why aren't people more supportive? Now I realize a lot of girls are just helping with body image & trying to help those girls wanting to lose weight feel better about themselves, but is that really helping? Again I'm just wondering I'm not wanting to offend anyone! Because I know when people see skinny girls they tell hem to eat more, so gain weight. Why is it so taboo to encourage someone to lose if they're wanting to?