Why do phones only go up to 5.7 inches?

Samsung Galaxy Note 3: 5.7 Inches

Samsung Galaxy Note 4: 5.7 Inches

Samsung Galaxy Note 5: 5.7 Inches

Why? Is it because it's to big to be called a phone anymore? Or it wouldn't fit in your hand/pocket?

This isn't only with Samsung Galaxy Note's.

Read more: Why do phones only go up to 5.7 inches?