The good thing is - at least they're being responsible and try to sell him rather than just give him up at any shelter. I'm sure the owner wants to see him go to a good home, otherwise, they wouldn't be spending so much time and effort into advertising him on any ads.
Many people often have their own reasons. Some we just understand, but some of those reasons are something we'll never get.
Many people do many things in their own way. Either it might be a good thing or a bad thing, but many times, as an outsider, people just have no rights to judge... at least so quickly.
I understand your concern because as a dog lover, many of us here hate seeing ads as such. I hope my opinion doesn't step on anyone; especially to you chihuahua lover, but this is just how I feel about many ads that I come across and see similiar to the one that's posted.
Linda and Tiny