I would have thought smoke would get into the rooms if there's really no walls around it
it's a simple matter of draft, and is the same way the traditional home brick fireplace like this works:
once heat is generated, and if the chimney goes high enough, an updraft is generated which is where all the smoke from combustion will go. In an open on all sides wood burning fireplace as long as the fire [pit] diameter is smaller than the chimney hood above it then all smoke will travel up that chimney. If you got a strong wind within the room then it can obviously blow smoke outside of the chimney draft and get into the room.
The protective screens... for wood burning fireplaces or pits is likely needed, and probably required by building code. Per your first pic of a traditional home wood fireplace, they usually do. I can remember embers from crackling wood flying out 5' onto the carpet even through the wire mesh screen, which is probably what led to the glass doors.
Place like a ski lodge, with a big concrete wood fire pit in center of room, with concrete floor and no combustible material near it, and a ~5' distance preventing people from easily getting next to the fire, is the shield. The updraft works the same.
gas fireplace with fake wood (which is what your pics are) produce basically no smoke the draft would work the same way which is where all the CO and CO2 and other clean combustion gases would go. I doubt those pics are of wood burning center room fireplaces... the type of people owning places like that would never dirty their hands touching cut wood much less carry it inside, those are gas fireplaces so it's much safer than wood. So that's how you can have an open design fireplace/firepit in the center of the room open on all sides, it's either natural gas or propane. And then I would assume local building code would provide various requirements as to what's acceptable.