It sounds to me like the lack of timing variation and note dynamics make it sound robotic.
Added to this, I think the faster you go, the more it sounds like MIDI anyway. Here’s a human demonstrating that :
https://youtube.com/shorts/jMhRdSgXzNY?si=05oGl_ZgM9qnqxDG
https://youtu.be/D2r428egsvc?si=iXKWwC5FQDIobSUa