That’s certainly one cause.
My mother only started thanking and please-ing us a few years ago, after her best friend threatened with breaking off the friendship then and there “unless you start offering to your children the same basic politeness that you’d offer anybody else!”
Mom didn’t even understand why: “but they’re my children!”
“They’re human beings! If you need them to do something for you, you say please, and if they do something for you, you say thanks. It’s very basic!”
“But they’re my children! It’s their duty to do those things!”
“So help me God, either you start treating them like you have any manners or this is the last time we have coffee together!”
She does it (we do remind her sometimes), but she still doesn’t understand why. She simply doesn’t perceive us as independent human beings - you don’t thank your car for starting, do you?