Critical thinking is a process by which we analyze a number of facts in order to make a judgement about them. In order for us to think critically, we need to be rational, skeptical and unbiased. Moreover, this is an extremely individualistic pursuit. Critical thinking needs to be self-directed, self-disciplined, self-monitored and self-corrective.
The fact that the exercise is so individual makes it difficult to pursue in an environment where everyone is similar. This is because standing out in such an environment can be scary, dangerous or even impossible. If we are only taught one way of thinking, we might struggle coming up with anything different. Moreover, we might feel pressured to agree with the majority in order to avoid conflict.