What is the deep reason why Ip Man is unwilling to teach Bruce Lee all Wing Chun and wooden stakes?

. Ip Man has a video of a virtual pile. At first he opposed it, but later he agreed. I think it may be because the old people were too conservative, and people in those days were very traditional, otherwise China Wushu would not have been lost so much. As for why he refused to accept the exchange, I don't think it is necessary to explain. Ip Man is at least an expert and has read books. What's so hard to understand? Because Bruce Lee is an American. Don't want to teach him.