Franklin once invented a new heater. Why didn't he apply for a patent to earn money for himself?

Franklin once invented a new stove, but he didn't apply for a patent to make money for himself. Instead, many blacksmiths made many new stoves and sold them to other places, making a lot of money. Friends didn't understand this and blamed Franklin for not benefiting young people, but Franklin replied without hesitation: "In our life, many things were invented by others and we benefited from them. Now that we have invented them occasionally, we should do them for free. "