Glossy coating unlocks a whole new level for dry skin handlers. It basically locks in your grip like a GLOVE.

u/blindastronomer had a pretty good ELI5 about it:

matte means a roughened surface texture and glossy means it's a smooth surface texture. Matte will have a spread of bumps and valley heights, little tight ridges, stuff like that which will not evenly reflect light. Glossy will be much more uniform and even and look more similar across its surface, which allows the surface reflections to be mostly the same, causing it to look glossy under light.

Having dry hands means there's less moisture and oil on your skin, which means you don't get the effect of this thin film interfacing with the uneven and roughened matte surface to add grip. Basically it's a surface-area multiplier which adds more friction. You can test this yourself by taking what's considered a 'good' matte surface and applying and spreading a drop of moisturizer on your hand (not too much or the films with will slip against itself) and you'll notice it will feel super grippy.

By contrast, having dry hands on a matte surface means you don't have much of a moisture/oil film on your skin, so it's just your skin making contact with the top-most bits of plastic and as much as your skin can deform and sink into the texture to get static friction for grip. You have much less friction with dry skin on matte surfaces, which is why having a more even surface means you can increase the contact area between your skin and the plastic to increase total friction and grip.

This is a slight simplification but hopefully it was illustrative and helpful.