Why is it so many Chihuahua that is in shelters?

Unfourtnately they have been very overbred, everyone thinks that they would make a great pet to carry around in their purse but then they realize that they have to train this little thing too. Then they end up in a shelter, because some stupid kid didn't know what they were getting into. People also like to breed their own pets and Chihuahua's are a very popular breed.