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What do you mean zinc chromate doesn't prevent corrosion?
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Exactly what I said.
Chromate is a surface treatment which acts in two ways; it protects the surface to some degree, and in some applications can serve to aid in retaining anticorrosive agents. What you're likely used to seeing as zinc chromate is a surface paint, although some people mistakenly refer to it as a chromate conversion (something entirely different), which is another process that converts the metal surface through a process of chemical change and oxidation.
Chromate conversion is better known as alodine, which is a much better method of treating aluminum surfaces than simply painting with zinc chromate paint (often used as a primer).
If you've had much experience around older airplanes that had zinc chromate (the real stuff; not the green spray paint that's sold today as "zinc chromate), you'd have seen it peeling and ineffective. It's no longer a barrier, it's not providing surface conversion, and it doesn't account for numerous forms of corosion (including those that form under surface coatings, such as filiform corrosion).
Some aircraft that have used surface sealants and treatments experienced increased rates of corrosion . If you've ever worked on Sabreliners, for example, you'd know exactly what I mean. Further, chromates do nothing for electrolytic corrosion in many cases, especially between faying surfaces, in bolt and rivet holes, and between layers, lap joints, etc. Surface paints and chromates don't prevent intergranular corrosion, fretting corrosion and other associated metal weakening and loss; in fact, where mechanical corrosion occurs, it removes the chromate.
Most aluminum comes with a surface of pure aluminum, sometimes referred to as Alclad. The alclad oxidizes, and provides a corrosion barrier to the underlying material.
spraying down the inside parts of your airplane sounds good, but doesn't stop corrosion from happening.