There is a theory of physics called "Relativity", but it has nothing to do with this discussion.
As to "why" questions and "what purpose" questions being "relative", I don't know what you mean. "What purpose" can be answered only by seeking out the "purposer", and then asking him/her/it (since "purpose" is not an intrinsic property of anything, but an extrinsic choice of the one qualified to make that choice (the "purposer")). For example, a cardboard box can be used for any number of things (container, fuel for combustion, home...) and these "purposes" have nothing to do with anything intrinsic about the box, but are assigned to it by its purposers.