You could replace "not believing" with "being a gullible idiot" and all of what you just wrote would still be true. Your developer will leave if they are offer

You could replace "not believing" with "being a gullible idiot" and all of what you just wrote would still be true. Your developer will leave if they are offered a better paid position at another company. It's because that company values them more. "believing" is just more nonsense thrown at inexperienced developers who don't know they are being hoodwinked.