It does keep the tempo, but also limits you to a single scale. So it does sound nice for a bit, but the song doesn't really go anywhere. There are some physical instruments that typically limit you to a single scale too, like a harmonica.
You don't need modulation (going to more than one scale/key) for the song to "go somewhere" or be hella interesting, catchy and touching/emotional.
Tens of thousands of the most known rock and pop songs and hits, from rockers to tearful ballads, are single scale diatonic as well.
You don't even need off-scale passing notes...
The reason this doesn't go anywhere, is not because it's single-scale, but because the melody has no direction and purpose. It's just a "random" pick based on the mouse movements.
