BeamNG is hungry for memory, and afaik became only hungrier with some update last year or so. And it’s generally not very fast, and been so for ages. I doubt it will ever be optimized, they’re probably just betting on hardware outpacing it.

The game has a bit weird architecture where every onscreen widget is a Lua script, and they all communicate with the game via the network. Scenario scripts are done the same way, from what I understand. Although Assetto Corsa has Python and Lua widgets running without any hiccups, so I guess BeamNG’s engine is just heavy.