>>1263024a myriad of reasons, potentially
in ohio registration costs more for a normal boat than for a kayak
registration on the trailer costs, too
maintainance on the motor
storrage space, the kayak can be tucked in to the corner of a garage while that takes up substancial space in a garage, and if left outside could be easily stolen.
ease of transport. if he just has a little car, imagine what it would cost to either get a trailer hitch installed or to go as far as to buy a completely new vehicle just to transport it when a couple pool noodles and ratchet straps are all the kayak needs.
locational use, a john boat can be a pain in the ass in small creeks because it's hard to just muscle it over a log jam where with a kayak and a good paddle you sometimes dont even need to get out to drag it over something, and a sit on top kayak can be much more reliably taken out in salt water than a john boat.
ease of launch. with a john boat you will very often need a proper boat launch, where with a kayak all you need is nothing to a strong piece of rope. a kayak can be launched off of a steep river bank (like, 45 degrees steep if not more) if you tie a piece of 1 inch rope to it, lower it down hand over hand, tie the rope off to something, use the rope to decend with your gear, climb back up, untie the rope, and then climb back down. getting your shit back is basically the same operation in reverse. doing that with a john boat will be a lot harder because you will need a wide straight gap, an extra person, more rope, and so on. i'm not saying that a kayak is better or worse as a whole than a john boat like your pic, im just saying that both have their applications and what is better or worse for an individual is situational in the same way that a bolt action 30-06 isn't inherently better than a 45 caliber pistol, or a pickup truck isn't inherently better than a honda civic, but one is definitely going to be better for a particular person.
