question about homemade dollies

i was looking at bh photo and i noticed all the dollies are arranged in a triangle fashion with three point of wheels, but all the dollies i've seen here that are homemade are in a square with four sets of wheels. is this jst because it's cheaper and easier to make or is there some other reason for this?
 
3 weel dollies are normaly designed for just a tripod.

4 wheels are not only normally stonger, but are quickly much larger alowing space for an operator or 2 (or 3!) as well as the camera mount, which can be a tripod, or a jib etc. And other gear (liek a seat for operator, a monitor, etc.. )It's also easy to make "bump smoothing" devices for 4 wheels than 3.

- Mikko
 
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