I think it is an old etiquette thing because it looks like your family is just wanting gifts. But I think most people don't pay attention to that "rule" anymore. My MIL is hosting my shower for her side of the family. In my opinion, if she is willing to host your shower, let her.
It is an old etiquette "rule" and also is the same for bridal showers. Moms and sisters are not supposed to host the shower. My mom would never consider hosting either of my showers (she is old school) so my aunt hosted my bridal shower and girlfriends hosted my baby showers. Like the pp said...it makes it look like your family is requesting presents (much along the same thinking if the person hosted their own shower).
Old rule and I don't know anyone that goes by that anymore. My mom hosted mine, most of the shower I have been to the mom has hosted unless she was OOT and wasn't attending.
Old rule, especially in the northeast. It seems to be a bigger etiquette issue in the south. I don't know anyone who had a bridal or baby shower that WASN'T hosted by their mother or MIL.
Re: My mother