My guess is that this is similar to StackOverflow switching to HTTPS [1]. Once you get to a certain size, something seemingly simple like turning on HTTPS or detecting desktops and redirecting comes with non-trivial problems. I can only imagine all the nuances that have to be addressed when you're serving the fifth largest site in the world [2].

[1] https://nickcraver.com/blog/2017/05/22/https-on-stack-overfl...

[2] http://www.alexa.com/topsites

Personally, I love that Wikipedia doesn't coerce you into the desktop or mobile version based on user agent. Being able to switch to the (somewhat more complete) desktop version when browsing on a phone is invaluable.

Sure, I mentioned that they could put an override, but sane defaults would be good. I don't know how many people actually mean to visit the mobile version of WP on the desktop when they follow a ".m" link, but I'd wager that it's pretty damn low.

> Completely off topic but I don't understand why wikipedia doesn't simply select the desktop/mobile version of the website based on the user agent

It actually does, but only when deciding to show the terrible mobile site instead of the desktop one. Even on a bloody iPad.