Good luck getting a fisherman who is just paddling or slowly trolling along a lake shoreline to wear a life jacket. When the water is warm, they’re not going to do it. Even when it’s cold they probably won’t, although they should.
It’s a no brainer when you’re paddling in a river with current or running a powerboat in a lake or salt water.
At least they should wear a floatation belt. Not technically a life preserver but it may keep you alive if you can stay conscious.