It's not garbage collection(although that's a part of it, but Unreal3 actually had a GC). It has to do with memory layout. Cache misses = lost performance and

It's not garbage collection(although that's a part of it, but Unreal3 actually had a GC). It has to do with memory layout. Cache misses = lost performance and being able to structure your memory appropriately is super-important. Look up Mike Acton or any of the Data Oriented Design stuff for more details.