The curious word 'why'

The same little word "why" may be used to obtain a causal explanation ("by what process has X come to be?") or a goal ("what purpose does X serve, as a part of a larger mechanism?"). These are obviously quite opposite ways of looking at things - backwards vs. forwards in time - one of them neutral, the other postulating agency. So I wonder, why does the word "why" combine both meanings and what are the consequences for everyday reasoning? Is it so in all languages, or do some exist in which inquiries as to cause and purpose must be represented by two distinct question words?