I've seen people on Lake Travis do the same thing. I usually find some that blow out of boats every summer. Probably not this year. All the boat ramps are closed.
We have a popular state park lake about 6 miles north of us, and we have a garage full of nice Coleman and Igloo coolers that we find along the road. I guess they bounce out of trailered boats or come out of truckbeds if the tailgate is down. Some obviously brand new, with a bit of road rash. :)