Crypts cannot spawn too close to the edge of the swamp biome. What that means is that smaller swamps and swamps that are long but narrow cannot have crypts. You need to find larger area swamps.

If you want, you can plug your game world into this website[valheim-map.world] and get a map of the entire world (with the option to show all crypts). Doing that would ruin the fun of exploration for me, but at the point you are at (considering leaving the game), it seems a viable option.