I believe it comes from low self esteem initially. Then finding their way into computers, where they then indeed have higher skills than average and maybe indeed observed that the job of some people could be automated by a shell script. So ... lots of ungrounded ego suddenly, but in their new guru ego state, they extrapolated from such isolated cases to everywhere.

I also remember the hostility of my informal universities IT chat groups. Newbs were rather insulted for not knowing basic stuff, instead of helping them. A truly confident person does not feel the need to do that. (and it was amazing having a couple of those persons writing very helpful responses in the middle of all the insulting garbage)