Let’s not pretend the acquisition and upkeep of chickens is free… if you eat a lot of eggs it is absolutely worth it, but there is some cost in setting up a coop, getting chickens, keeping chickens fed and safe from predators, disease, etc.
Plus you have to have property to keep them on and be allowed to have them on your property. For most Americans that isn’t possible due to lack of home ownership or HOA restrictions on what animals you can have on “your” property. (HOAs are bullshit)