A step in a sequence, and a raised place where things are shown. Both mean a position passed through and witnessed.
Vulgar Latin *staticum (a standing place), from stare (to stand), via Old French estage; a raised platform and a step in a sequence both take their name from a place one stands to be seen or passed through.
A position passed through and witnessed, whether it is a step in a sequence or a platform built for showing. Both mean the standing was seen, not only that it happened.