Why can't we say "informations"? [closed]

Solution 1:

Because we don't. I'm sorry, but that is the whole of the answer. Languages are as they are, not as anybody (native or foreign) wants them to be.

Solution 2:

Because information is a mass noun, i.e. uncountable. In the same way you would say give me all the water in your bucket, rather than give me all the waters...

For discrete items of information, you could use facts.