"Flash emulation in the browser – This is our final and most preferred solution. With all of today’s modern browsers supporting WebAssembly (a technology that enables high-performance applications to run safely on web pages), it is perfect for this task. While several emulation options are still in development, the ones we have explored currently support a small number of games and will continue to support more in the future."
I saw that in the link you posted. So my question remains; why doesn't this site have Gemcraft Labyrinth? This website chose one of these emulator things right? So if that's the case, then there really isn't a reason not to have Gemcraft Labyrinth.