I guess the answering word is ‘seduction’…
customer seduction for market parts. udk is an amazing engine but unity is still and always before.
Just like blender team, udk team did not understand that users number growth don’t come from useless ( but wonderfull ) features, but with a solid and exhaustive doc.
Every tool should respect this basic rule.
No doubt those amazing features present in UDK are the proof of devs competence.
Even if useless, they are a nice showcase and appeal to ‘easy’ customers.
as an example, in 2015, ubi-soft released a game called assassin’s creed unity.
As a dumb customer i rushed in shop and bought it as it was absolutely stunning.
Today, 6 years later, i’m still unable to make it run on my machines.
ubi soft hit their target: seduce people to make them buy the game ( even if it’s unusable ).
UDK is a very good game engine lacking of doc and i won’t be seduced by amazing features that almost bobody can run in-fine…
So i wait for other people to release gazillion triangles apps that can run on ‘common’ machines