There are quite a lot of ways of making an open world game with infinite replayability without requiring massive maps, but they're not in the style AAA gaming has been going for in the past decade, they're more things like Oxygen Not Included, Factorio, Minecraft or Battle Brothers were the game space is procedurally generated, the fun is in conquering the challenges of a map, and once you exhaust it you stop yet end up coming back months later and try a new game with a new map, from scratch, because it's again fun and there's no "I know this map" to spoil it.

The handmade game spaces with custom made "adventures" do manage to have better experiences than those games that rely on procedural generation and naturally emerging situations for providing gamers with experiences, but they're mainly once of and rely on sheer size to remain entertaining for long.