Why do parents dress there baby in pjs when they go out in public?

I did sometimes but only when my son was under 3 months and only because they fit better than clothes and it was cold when he was born, after spring came he was always in clothes. I guess some people are "lazy" and just think it's easier. (I personally don't think it's lazy before 6 months, we new moms are tired!) I do think it looks a bit tacky on older babies though unless it is late then I assume it's almost bedtime.