I cannot even think of a time when I have heard someone use the pseudo-word "informations." The only circumstance under which I can imagine its use would be in technical programming languages. For example, maybe a computer understands the word "information" only to mean one piece of information, because whoever designed that program defined it as such during programming. So, later, when people were using the program, they typed something about "information," and the program could not understand that they wanted more than one piece of information, so they just added the word "informations" to the programming and got used to using the pseudo-word in this fashion. Maybe these people think in the programming language so much that they used the pseudo-word in other contexts.
Otherwise, if someone says "informations," they either speak English as a second language and haven't yet grasped the difference between nouns that require pluralization and ones that are uncountable (as you put it,) or they are just very stupid English-speakers who probably have something severely wrong with their brains, because they haven't learned their own native language through hearing it. Grammatical rules are hard-wired into our brains. (Rules for specific languages, of course, are not, but the ability to learn the grammar of a certain language without any cognitive processes is.) So people who cannot figure out that "informations" is not a word probably have brain damage and had mothers who smoked crack when pregnant with their inbred babies or something. Oh, or maybe very young children would say "informations."
You really shouldn't ask why "you" or "we" pluralize "information," since I don't, and if "we" includes you, you should ask the people with whom you associate that you hear saying that, because, unless they are brain-damaged imbeciles, they know something that I don't. It could be some sort of slang.