The principle is not to preserve the nice packaging by sealing but to preserve the nice film
The main issue is the relative humidity that can affect the emulsion, to stabilise that the package must be sealed, (and at a "reasonable" room RH when sealed) Ziplock is suitable, so the film is not exposed to the environment within the storage . The film canisters are probably/may be sufficient but as there are so many types and porosity is not quoted it is easier and safer to seal them.
The OP very well described the RH effect on the packaging, the goal is to prevent the film suffering the same fate.
If you read the article quoted, which I admit is heavy going, you will note that the times to equilibrium of the moisture content (RH) vary with temperature so any problems may take months to become apparent, and BTW it's not my advice it's the advice of much more experienced and clever photographic emulsion engineers than I at both Ilford and Kodak (although Kodak make it difficult to access much of their useful technical data these days, using Kodak as a generic term as I suspect the various parts are not working as closely together as they should and responsibility seems uncertain for much archive material as they are split into many separate corporate parts)