Scan finds lots of bugs for open source projects at no cost. Sure it is marketing, but unlike most marketing it also has real value.
Not sure I can comment on the results on your own code, but I will say that volume of results is not always correlated with value in static analysis. There are plenty of noisy rules that basically have negative utility if you factor in the time it takes to review each issue. It's a complex balancing act between finding more issues, having fewer false positives, analysis time, understandability of results, and other factors.
