Here they are...
1. Being amphibious, you could get from your boat to shore quickly, and then proceed down the road/trail to the store for provisioning.
2. If you were ever chased by bad guys on land, you could just head out over the water. (Unless the bad guys were on snowmobiles too.) Ditto for being chased on the water.
3. It might confuse the watercops who are trying to fill the towns coffers.
4. They are probably cheaper than hydroplanes.
5. You'd look really cool out on the water and get invited for sundowners everywhere you go.
6. The powerboaters would accept you as on of their own. (Perhaps of marginal benefit, but worth listing.)
7. As a new one-design class, it would be more interesting to watch than lasers or sunfish.
8. No one would steal your dinghy engine off the beach.
9. They are easy to move up the beach, to get them above the high water line.
10. They work in winter too.