Yes what desi said.... Plus your abdominal muscles are already stretched and tore from previous pregnancies too. This is my 3rd, i am going on 12 weeks, and already showing.
Same here i am 23wks second pregnancy and im bigger than first one. I feel fat but it is what it is.
People usually show faster because the uterus has already been through the stretching and stress of a baby growing, after your first pregnancy your uterus is more flexible, therefore its easier for it to stretch and grow again
With my first I didn't show until I was like 7 months. With my second I was huge. Everyone thought I was pregnant with multiples. It was hard. With my third I'm not as big as my second but I'm bigger than my first. I don't know why but people often show sooner with their second.