Why pontoon boats are typically not being trailered?

Lack of a decent trailer. (also if you have flimsy furniture it won't make the
trip)
Pontoon boats usually don't have a decent bow hook to pull them up on the
trailer with. A common type of trailer fits between the pontoons and only
provides about 4 feet between the wheels. These are unsafe at any speed. You
can get a regular boat trailer with ~7' axle and rollers or bunks under the
pontoons that will do well on the highway. You can also rig a bow hook but it
has to be connected to a stringer that runs down the deck far enough to be
pulling on several cross ties. Mine is 2 pieces of 2x2x1/4" angle 8' long under
the deck, an inch apart with a 1/2"stainless bolt between them for the hook.
I take my boat to the Keys and other places but I did have a learning curve to
find a good trailer and learn how to load it.
Tie this thing down well !
I use 3 load binders like you see on flatbed trucks.
One tip, be sure the bow trails lower than the stern, it keeps the boat from
flying. Mine is about 15 degrees from level and it trails true at Florida
"interstate speeds" (80 or so) although I don't recomend trailering anything
that fast.