It's a bit less polished, but far, far better when it comes to hacking. I found it significantly easier to create a mod for Minetest than to use a mod in Minecraft. Once my kids grasped the idea that they could add whatever items and behavior they could dream up, they really took a shine to it. The Lua coding used is very approachable.
The only issue though, is that I think a lot of his motivation stems from potentially sharing what he has made - pretty much everyone his age has a copy of Minecraft.
One advantage that may help is not needing a license; if you have siblings that have to share a Minecraft account they can play Minetest on as many machines as they have without bugging their parents to pay for a new account. Plus it can run on much older machines.
But yeah, it can be a tough sell just because people don't want to bother.