In a context where you want to have software built by different independent developer teams working on the same persistent world objects, you can't expect them to collaborate on programming style and coordinated libraries, as is done in industry software. Any unexpected side effect or variable aliasing in another library may ruin your runtime execution.
Pure functional programming avoid this by forbidding side effects, but forces a programming style where all state updates need to be declared and carefully handled by the developer. Functional reactive programming (spreadsheet-like updates) is being used a lot in the web to ease that problem (all popular frameworks have a version of it), but it is best suited to processing client/server updates, not full world simulations.
Verse approach seems to bring new expressive capacities suited for dataflow programming, allowing data transform logic to be built with functional expressions and separating these from the techniques needed to link one component to another.
Most programming languages I can least understand the general gist, the core motivation, whatever.
I have a lot of respect for Epic Games so I read through most of it but I have to say I'm still non the wiser.
If forced to summarize I'd say.. it's some kind of Haskell-ish language where the types themselves are defined by ... runtime functions? With some attempt at also being a prolog-ish logic language?
But why?