Mychal,
But you probably think it is reasonable when the reverse happens: a pet owner gives his pet to a friend to take care of for some period of time in the other person's home. The pet still "belongs" to the owner even though he doesn't have any contact or derive any benefit from the pet while it is in the care of the friend. I even know cases of this where the pet-sitting occurred for as long as a year or more. There was a situation of pet-sitting that was in "The Ethicist" in the NYT in which the pet-sitter was walking the dog and the dog got into a fight with another dog requiring vet bills. The owner didn't want to pay the vet bills because he said it was the pet-sitter's fault for not keeping the dog on a tighter leash. There were questions of ownership and related responsibility.
Although "selling" a pet is more of a fictional sale than the selling of chametz, particularly because you can't put the pet away in a sealed and marked container, the reasoning is similar. Another similar situation is the "selling" of agricultural land in Israel during the "
shmita" year.
Strict interpretations of Jewish law can make life difficult, so observant Jews use many workarounds that may seem ridiculous to others. I've read about people who accuse Orthodox Jews who want to erect an "
eruv" as "trying to cheat God". But many atheists think that
all religious ritual is ridiculous.
The problem with the milkbone is not whether a dog owned by a Jews can have it, but
whether the Jewish dog-owner can own the milkbone before he gives it to the dog. If the dog could go to the store and buy the milkbone for himself, that might be different. There is no problem if a Jewish dog owner leaves his dog with a non-Jewish pet-sitter who feeds the dog a milkbone.