What you need to keep in mind is that foods cannot be called GF, unless they meet the GF standards. A food such as Jello, is GF in its own sense ... however, unless they can guarantee that it is manufactured in a plant where all is GF, then they can't make that declaration for safety's sake.
Likewise for products stating they are nut-free. They may be ... but if there's a nut anywhere within the facility, then they can't make the guarantee, and you'll often stated on the packaging that they are not making that claim.
We have an ice cream company here that has some ice cream that is GF, nut free etc. and some that is not. And people wonder why some are? and some are not? Simple enough ... two plants where one is kept "clean" and thus the labelling ... and the other infiltrators are kept to the other plant.