Is it normal for people to donate underwear?

I’ve often wondered this. Growing up when my mom would donate old clothes she always tried to donate underwear but my dad always stopped her. I’ve also had a few friends who regularly bought thrifted items as the only option but specifically said they don’t buy donated underwear. I’ve gone to thrift stores and have never seen underwear there. Is it bad to donate underwear or weird? Do donations throw them away for sanitary reasons?