Is it possible that the sample you're observing is changing? As people accumulate experience and begin to regard themselves as competent, then expert in a field, they have a greater stake in defending that status.

It's my observation that in the aggregate smart young people are more amenable to criticism than smart older people: i.e. there is a bias toward defensiveness that, if not actively defended against, becomes increasingly evident as people age. Maybe you're noticing the behaviour of older people now.