“Regular” peas are are still harvested immature only at a later development stage. Fully mature peas are very hard like a dry bean.

Sweet corn contains gene mutations that reduces the sugar to starch conversion in the kernal. So the sugar builds up in the kernal instead. The varieties are classified by the gene or combinations of genes they contain (su, se, or sh2). When the seed is fully mature and dry the seed looks like a raisin because of the lack of starch