> so building a custom distribution to include, say, Magit,

I mean, you don't need to really "build" anything, you just need to install the package:

  (add-to-list 'package-archives '("melpa" . "http://melpa.org/packages/") t)
  (package-initialize)

  M-x package-refresh-contents
  M-x package-install magit

What would happen if you did that?

this sounds a bit crazy.

It is unfortunately common.

Any organization with high-value data has a responsibility to try not to be the next Equifax.

Programmers, sysadmins, and DB admins are excellent targets for attackers.

So, it's not actually so crazy to require that all tools be vetted by internal security teams, especially third-party extensions for Turing machines like Emacs.

I love Emacs but its architecture is a nightmare for Blue Team, and the easiest stance is definitely "no installing packages", or just "thou shalt use this IDE and no other".

I get that, but the right approach to securing high value data is to secure the data, not try and control every aspect of the environment it lives within; that's often more security theater. Note I'm not suggesting that the right approach is "wild west", rather that any vetting process that doesn't allow for well established and widely used tools to be adopted is probably too rigid.

I didn't say the "right" stance was to ban extensions, just the "easiest".

Since humans default to lazy, I thought that clearly explained why the phenomenon happens.

Perhaps I should have been clearer that I don't think it's the ideal approach, even if I understand where it comes from.

In my experience of US corporate culture it's also unfortunately common for employees at all levels to kowtow unnecessarily to "legal" without considering whether what "legal" are saying is sensible or not.