Which is why what the military uses for unstable terrain is treads like you see on tanks. Same for construction equipment that operates on soft soil.
Like, some caterpillar-type vehicle could move fine on that beach, but you'd definitely see the trace of its movement afterwards...
So legs are not a useful movement mechanism for tanks, but they might be for delivery bots, etc.
I also wonder about the energy expense. The strandbeests seem to be powered by nothing else than a number of sails and the movement mechanism has little enough resistance that the wind force is enough to pull the vehicle along.
It feels as if a caterpillar would have more resistance, though I don't have the numbers. I guess you could in theory make a wind-powered caterpillar vehicle by using a turbine - but the vehicle would probably be slower, I.e. less efficient?
If you wanted to build a similar contraption that is powered by wind but moves on wheels, I imagine there is a much larger chance of it getting stuck.