Answers to the question How do they decide the key? point out how useful it is for a jazz musician to be able to play a piece in any key.
So, in jazz, why does sheet music give chord symbols with absolute, not relative, roots? Chord symbols with absolute roots reinforce the association with the particular key represented by the notes, and make it harder for the player to learn the chord sequence in other keys. (At any rate, up to the point where the player has memorised the piece and thus doesn't need the sheet music at all.)
Traditional chord notation (I, V etc) is relative, so absolute-root chord notation represents a change from tradition.
A theoretical discussion of a particular chord progression (independent of what pieces use it) may use relative chord notation, but I'm thinking here of the notation of the chords for particular pieces.