Likewise here with a Samsung Galaxy S that lasted 8 years, without a case or cover. Plenty of dropping on all sorts of hard surfaces, no cracked screen. Some of the finish started smudging off on the back though. I have no idea what people are doing to cause such damage.
(Only ended up replacing that phone because it started just not picking up calls and texts for days at a time)
Well, my friend's S7 cracked itself overnight. My S4 cracked twice due to dropping it on the floor, both times I had the screen replacement. My current S7 fell frequently, but is still mostly intact. As far as I can tell, everyone in my immediate family cracked their smartphone at least once over past few years.
Beyond dropping, as far as I can tell, there are two other common causes of screen breakage. One, sitting on it (a lot of people carry their phones in their back pockets, which is something I cannot understand; beyond accidents, this makes them vulnerable to pickpocketing). Two, women sometimes crush their phones in their purses (especially when they are in hard covers that act as levers when an item gets between it and the cover).
(Only ended up replacing that phone because it started just not picking up calls and texts for days at a time)