The longer length (20feet?)and tri-axle probably make a huge difference over a 2 or 3 foot long single axle dolly.
I know my 16 foot boat trailer is considerably easier to back up than my 8 foot long utility trailer.
Like I said, Larger scale but same physics. Along with a shorter dolly tongue, one is using an ATV with a shorter wheel base. Pat K understands the physics.
You can back up with the 2 wheel dolly but it is a different technique or skill set that you use. Anybody that grew up on a farm knows it’s easier to back up a single pivot trailer like a boat trailer or manure spreader than it is to back up a trailer with pivoting front wheels like a hay rack, grain wagon or you wheel house with a 2 wheel dolly.
^^^^^^^^^^ nailed it! ^^^^^^