Browser engines are probably some of the most optimized pieces of software in existence, so it doesn't surprise me at all.
Love2D uses Luajit and directly calls established game libraries. The CPU usage should be far better for 2D games, luajit is faster than a browser's javascript jit. You can also create single exe games that are a few megabytes and not a few hundred megabytes.
Explain this to electron haters.