easier with assets. But assets are not rated or required. :D Also depends on the engine and if game is playable in browser and other stuff.
I imagine it as a “puzzle”, where you share your solution and check others solution. And later you can easily reuse it (or others). But if game is not playable in browser or altogether, then people might compile it locally to check and not having any assets may be a problem.
I personally use Kenneys assets. There is extra point for asset consistency. Like if they assets play together well. So photo-realistic high poly model in voxel world won’t get a point. But text-based full ASCII game will.
If you have specific assets that you don’t want to share or they are very big before game build - you can add them to .gitignore file.