Kinda like gatherings at houses...Multiple households were already banned, and everyone was ignoring those bans, and the DNR couldn't keep up with fining people... so they banned motorboating all together.
...and why only motorboating? Because 99.9% of the boating being done that time of year that involves multiple households is motorboating.
It ain't large sailing yachts full of people. It isn't 3 households in a kayak.