I think, what both of these tile sets are missing, are small details, that make them believable to be real. They are just very big blobs of one color, without any small detail, or something in there to show it exists there by itself. And is not just there for the sake of it.
Like some rocks and worms in ground. Or clouds and birds in the sky. Cracks and crevices in the house. But most importantly, it is also lacking shadows, and gradients. Nothing is just one color in real life.
You can look at some example assets that are somewhat similar to yours. These are mario like asset They don't have too many details, but they do have enough, to show that they have details.. Or these basic assets That do not have any detail, but the artist has made sure to make it irregular at least.