“So I guess in your case it’s the Jewish Esrog sellers that make sure each year that esrogim. Are being planted by the millions etc… And not forgotten”
That’s exactly right.
The esrogim we buy are grown in Jewish orchards. They have to be, in order that we can ensure that they are not murkav. If we didn’t need esrogim for Sukkos, there would be no reason for these orchards to exist. And since esrogim aren’t really good for anything else (besides maybe smelling nice), they would probably just go extinct.