Because most tablets are intended to be as thin and compact as possible while being too large to wrap a hand around. Imagine the complaints if Apple told people

Because most tablets are intended to be as thin and compact as possible while being too large to wrap a hand around. Imagine the complaints if Apple told people to buy a case so they could hold the product. Imagine putting a ledge on one side to hold it oh hey, it's a Kindle Scribe (and still ALSO has a bigger bezel than the iPad Pro.)