There's little evidence of ground stone tools until very recently [1], like tens of thousands of years ago. It wasn't until agriculture that the technology became widespread.
Knapping [2] - which has been around for over 3 million years at this point - is much more predictable and efficient than grinding while requiring less intuitive knowledge of the materials. Paleolithic people just didn't have the resources to experiment with enough materials to figure out hardness, grain size, etc. for proper grinding.
If you look at the video some of the patterns are very regular and geometric, not what I'd expect for a regular sharpening of a tool. It's possible they sharpened tools artfully but then that's just a different way of creating the inscriptions.
Knapping [2] - which has been around for over 3 million years at this point - is much more predictable and efficient than grinding while requiring less intuitive knowledge of the materials. Paleolithic people just didn't have the resources to experiment with enough materials to figure out hardness, grain size, etc. for proper grinding.
[1] https://en.wikipedia.org/wiki/Ground_stone
[2] https://en.wikipedia.org/wiki/Lithic_reduction