What's the difference between dried split peas and dried snack peas such as wasabi peas?
Recipes for homemade wasabi peas involve soaking, boiling, and then low-temperature roasting (essentially dehydrating) the peas.  Split peas are produced by simply drying the peas after they're harvested and then removing their skins.  So the reason is that the snack peas are cooked while the split peas are essentially raw.  The cooking process breaks down cell walls and makes the peas tender, even after they're roasted to draw out the moisture again.