Sorted. Caused by Bijan's masks.
I don't know what they are but, in general, any airport for MSFS doesn't include actual winter textures ( in P3D this is completely different ), it's the sim itself that figures it out the snow quantity depending on the tone and brightness of textures so, the more they look like aprons, the less snow they'll take, it's completely out of our control, the only thing we can do, is to specify that some object should never get snow, no matter what, but that's it.
This means, in general, if you don't have *any* snow, it *might* be the airport's fault ( the developer might have mistakenly enabled the "no snow" flag for all materials ), but if you have *too much* snow, it's either the sim, or something else.