Most people aren’t taught how to deal with criticism and see it as a personal attack, an attempt to discredit them.
A lot of the time that’s what it is though. Accepting criticism at face value takes a lot of trust because the main intention of the person giving it could very well be to assert dominance or persuade people to stop listening to you rather than give you useful information and help you improve. This is why people are afraid of criticism; it has always been used as a way to build social hierarchies, and it goes against our instincts to see it as not being about that.