From what I've seen on our UV web, the main disadvantage to UV is that you have a very small window for emulsion on press compared to conventional inks. It makes life a bit more difficult for the press operator. Let's face it, the most important fundamental operations in press operation is paper feeding and ink and water balance. Anybody can be mechanically gifted, but those are two core disciplines. And that ink and water is no small task.
Our experience has shown us, and maybe it's just our press, that it can take its toll on the blankets, rollers, and even plates and wear those items down faster than conventional. Even when the products are specified for UV use.
The main benefit of UV for us ( an in-house direct mail plant) is that it comes off press completely dry/cured so it can go right into finishing and get mailed the same day. Without UV, we'd probably be seeing an extra day of drying for our mailing products. With UV, we come right off press and directly into finishing.
That, and durability of the ink on the substrate (you're basically building a plastic coating on top of the paper) are the biggest product reasons I can think of. It's also got some environmental and press design gains vs. conventional methods.
It could be that your product doesn't really benefit you to be UV. A lot of the advantages are specific to the operations of the printer. Given that you're saying it's only paper substrates, then I'd guess your products don't provide you or the printer much reason to use the benefits of the UV if the cost is much higher. Plastic/synthetics would be a different story. Keep in mind, the UV press may cost them much more to operate than a traditional ink press, and that may be coincidentally the actual press, not just because of the UV ink used.
The other factor could be, and I only mention this because of where your profile says you work, maybe their UV production doesn't meet certain FDA approvals vs. conventional inks. It may not apply to what you're ordering, and I kind of doubt it would be the case, but who knows? If it does have something to do with the decision, it could just be that they simply aren't "approved", even though the process may be just fine for that use. I'm not sure how all that food stuff works.
Lastly, the decision to stay away from one vs. another could be based solely on profit margin. The conventional may have a higher margin for them. Who knows? That's one question you'll never know the answer to.
