1. Pet stores only care about $$$.
2. Therefore, they usually don't take good care of them.
3. They are sometimes sick or pregnant because of the lack of knowledge to separate the genders, and to quartantine and take care of the sick.
4. If they're sick, they just count them as "casualties" or "lost stock," like a stolen CD ro something. (Why would they lose money by taking them to a vet? They're just merchandise.)
5. They get them from breeders who only care about $$$ and don't provide the greatest care.
6. Your money goes to support this cause.
7. Because of this, there are more cavies that meet this fate in the long run.
8. Because more of a difference can be made by stopping the whole operation, and more cavies can be saved by taking a stand rather than saving a couple at a time. In fact, by doing so, you are giving that monye to the breeders, who sell them to stores, etc.
9. Also, it's not as if they screen you to check if you have good care planned out.
10. Many are not knowledgable about their pets, but they act as though they are, giving out awful advice.
Hope this helps you understand. This is not 100%, but it is the vast, vast majority of stores.