Controls are remappable (although up for jump does prevent up from working in the menus... maybe that's something I should look into changing in the post-jam version). But my experience has been that usually platformers have jump on the opposite hand from movement (thinking e.g. Mario, Sonic, Mega Man, etc.), and Z for jump is consistent with the computer platforms I've played (e.g. Freedom Planet, and I think Celeste's default control scheme is around that same area of the keyboard) which is why I chose that.