Why do customers do this?

I’ll never understand how someone can place a order then straight up ignore shoppers when they try to contact them. I get it sometimes people get busy but there’s no way no one doesn’t check their phone in 20-30 minutes while i’m shopping for them. It’s been happening too frequently and it’s frustrating because i’ll then make my own judgement call on a replacement or refund then after I checkout they magically learn how to respond. Anyway, this happens a little too much to me how about anyone else?