Why doesn't UE utilize STL containers?

Epic:

This makes porting to Unreal (as a 3rd-Party lib) a lot more difficult than it should be. Supporting an industry-wide standard isn’t asking too much IMO. Making it impossible to port without a substantial rewrite is an unnecessary obstacle. I would add that it is also contrary to the goals behind the (commendable) openness you have recently embraced.

My job just got at least 10x more painful. I have to reevaluate if it’s even worth the effort at this point. Please consider future support.

It doesn’t look like there are naming conflicts, so why can’t there be both stdlib and your alternative?