How to sandbox in UA?

Ive seen many people saying they prefer to play UA as a sandbox, why is that? And does it work? How do you control the pacing/do not make it feel boring if the players dont find anything to do in the sandbox? And how do you do it? Maps? You make “random rolls” on the map for “random encounters”? How do you do it? They could encounter a major faction in a random encounter? Or instead of it being a randomized thing you as a GM choose when to introduce? Do you roll randomly for events and unnatural phenomena also?

Thats just my experience with sandboxing other RPG, ive used random rolling to determine everything and just describe how the world reacts to them. Is that how you guys sandbox it? Or is it more like, they are there and there’s a lot of conspiracies you throw at them until they bite one?