Lmao WHAT? It's just a big empty map with no actual reactive sandbox elements.
You do realize if you hit Tab in Sandbox mode, it opens up the editor. From there you can build structures, make scenes, import custom models and textures, use various tools to create rudimentary triggers and game logic, and more.
Or, if you don't want to make something from scratch, you can find plenty of user created maps, scenes, outfits, poses, objects and more on the official Discord (which you don't have to be a Patreon member to access btw) that you can simply download, slap into the AutoImport folder, and load up in game with zero effort.
Some people have even made entire mini games. I myself am working on a side-scroller mini game map inspired by Parasite in City. Due to some tool limitations it's a huge, time consuming pain in the ass to actually make a combat system from the ground up and have it work the way you would expect, but it is entirely possible.