Easy to grow
I find beans among the easiest veggies to grow. Of course, I have chosen varieties that are suitable to my local area. Most of these varieties go through their cycle in 90 days or fewer, so they can fit within the demands of several cover crops and complete within the limited growing season.
Easy to save seeds
And the nature of beans makes they safe and easy to save for planting in future seasons. Beans are self-pollinating and aren't subject to cross-pollination by bees. (There may be some exceptions to this based on the shape of flower that may allow pollinators to do their thing.)