a) Most of them are ugly to me. I buy bags that look good.
b)The point of a designer bag in most cases is to say "I am rich. I can afford this." So if you can't, really, what's the point?
I buy for my body. If it looks good, classy, and cute I'm buying it. Fashion is fun from an artistic standpoint, but I don't feel the need to blow a paycheck on a brand name.