I would think the company that owns the brand wants to control the information about their pet foods rather than some company that only manufactures for them. If a co-packer posted the different companies they make food for people might expect them to provide info for the different brands they make food for.
There are some brands I won’t buy because of the co-packers they use. Being affiliated with certain co-packers can also affect business. Another reason a pet food brand might not want their brand posted on the co-packers site.
