Probably Apple decided this based on screen size and thus, perhaps, according to them, ergonomically its an improvement or necessity to do that? Dont know.
All I know that I wish there was an option to get Microsoft Windows onscreen keyboard our household Surface Book 13.5 has, that keyboard is so easy to type on even not looking at it all the time, unlike any other iPad keyboard Ive typed on which is a chore to do, 12.9 iPP here. At least for me.