They have no idea how to do accurate estimations other than guessing, or giving in to a management target date and not understanding the difference between targets, estimates and commitments.
The next step is nearly always, rather than learn to be a good estimator, to declare that if they don't understand how to do something, then no one does.
The idea that if you haven't bothered to learn how to do something, no one has, is an amazing act of hubris and is characteristic of a certain sort of person who often causes more damage on a project than contributions.
The solution is to either stop giving bad estimates based on nothing, or to learn to do it properly. Giving bad estimates because you don't know how to estimate is a form of engineering malpractice. Declaring that because you are an incompetent estimator and have not bothered to learn how to do it that therefore no one else can estimate either is pure immaturity. It is similar to the principle of object permanence where in Piaget's theory of cognitive development he notes that where infants from birth to around age two don't believe a ball exists once it leaves their field of vision.