Being wrong on the internet is vastly more impersonal than being wrong in person, as it were. The urge to correct is similar in both cases, but in the in-person case you can suffer clear consequences from others' wrong beliefs (eg. if they are family). There's some overlap with #3 -- consider the common case of the presumption that you are heterosexual and cisgender.

There are also people who say things they know are wrong in order to see what you're made of, if you're a pushover or not. Unlike the online equivalent (trolling), ignoring them is often not effective.

It seems pretty clear to me that not-correcting others can be a self-deceiving behaviour, at minimum.