The thing is: publishers need to sell something to people if they want to keep the lights on. Theoretically, that could also be pre-made adventures, setting books, etc., but from what I know, core rules sell best, and then we have supplements with new rules/player options, and then nothing for a while, before we get to adventures. So I suspect, we're stuck with the current approach of new editions every 5 to 7 years, because no one has found a better model so far (potentially because there is none).
It's arguably slightly better with publishers like Free League, because they usually give us new games instead of new editions (at least right now, Alien EE is IMO more of an exception than the rule in their portfolio).