To use real names is a requirement on some of the smaller public wikis.
Large public wikis tend not to have such policies, if only because they are unenforceable and prone to easy subterfuge, since no one is actually enforcing.
To have such a policy is effectively to remove outing problems except for those who actively defy the policy, who may be taking their chances by trying to subvert the policy.
However, it is also to deny the right to vanish, as comments made stick forever and will often be quoted out of context by liars and propagandists. This may have violent consequences.
If constant pseudonyms are allowed there are various problems with the assumption that "a single real person is writing that". It is very often not the case, as some trolls for instance foment ambiguity by sharing their IDs and IPs.