Quoted from the internet

“Kellogg’s [have] found that the zipper closures [on ziplock bags] sometimes “do not close properly or food gets caught in the seal,” and that their “current packaging set up just couldn’t cope with the addition of zip locks, as it would make the process much slower and more expensive.”

Diana Twede, professor emeritus from Michigan State University’s school of packaging, confirmed that cereal companies are reluctant to [use ziplock bags] because of the extra costs. So it is not a conspiracy on Big Cereal’s behalf to create a sort of planned obsolescence by making their product get stale (although companies in other industries have certainly been accused of doing so.)

If manufacturing an item becomes more expensive, a cereal company might then pass that cost along to consumers, who in turn might decide to buy a competitor’s product, said David Luttenberger, the global packaging director for market research firm Mintel.

Twede said that if a company decides to take the leap, they have [sic] no competitive advantage against their rivals.”

Proof positive that an oligarchy prevents innovation…