mrdux has some good insight, to which I will add :

Floating docks offer little to no cover, other than shade, unless they have brushpiles under them or weighted trees hanging off of them. Crappie suspending under floating docks are more vulnerable to predation, and easily visible to their prey. That's not to say that they don't utilize floating docks, they do ... it's just that stationary docks (on wooden poles) have this missing component (cover) in the form of the vertical wooden poles & horizontal crossbeams.

And, actually I HAVE shot docks on Barkley Lake, many moons ago, and with good success ... and I did report about it !! It's just that it was so long ago, that the report has been deleted due to the many format changes this site has undergone.

... cp