A few years ago you might also ask why would anyone give out $5 certificates? It's not any more work on their part - it's a extra parameter sent to their certificate generator.
With SQL Server, you can get the Express Edition for $0 or the Enterprise Edition for $thousands. But to build the Enterprise Edition, they actually compile it from the same source code without some #defines that enable various Express Edition data size limits.
They do less work yet charge you infinity times the price. Now that's a ripoff!