It can all be down to room shape and size. If you think about it, the fan produces a down-draught. This spreads out across the floor, up the walls, and returns to the fan. Because of the size and shape of the room, and size and shape of furniture, the moving air coming back to the fan is arriving at different speeds from different directions. When the fan blades hit this turbulent air, the force on the blades is constantly changing as they rotate, and so the fan wobbles. This makes things worse. Since the direction of the downdraught is now changing, so too is the air turbulence back at the fan . The whole process is cumulative, and in a smallish room could make even a perfectly balanced fan wobble quite violently.
There's no easy answer, since it's a combination of fan speed, blade size, and the rigidity of the fixture.