And some are mitigated by exposure. Cashew shell / mango skin / poison ivy, as an example.

It's what makes addressing it so difficult - we know it's an immune response, but don't understand the mechanism that triggers it.

Yep! New research couldn't come sooner - while luckily I'm not deathly allergic to anything, I have moderate reactions to a wide spectrum of environmental stuff. I got shots for years in my teens which helped a lot, but now I've noticed in my early 30's some of that immunity seems to be decaying.

Could that just be that health care workers are more likely to notice a latex allergy due to repeated exposure?

Somewhat unlikely. Latex is in LOTS of stuff you might not think about - like bath mats, baloons, etc. Even duct tape contains latex. Anything containing natural rubber.

Maybe there's a spectrum of responses and the people on the gentle end just don't have difficulty putting up with the symptoms unless the material is literally pressed to their skin for hours on end?

My hands feel slightly puffy and look slightly red after handling some types of rubber. I can wear latex gloves without issue, so that's not it, but if there are people who react to latex like I react to certain kinds of rubber then I can easily imagine the allergy going unreported.

True, but it's one thing to blow a balloon or stick a piece of duct tape, another is to use a glove for hours a day.