It's not. There seems to be some misunderstanding that these brands add sugar to normal drinks. They don't. Normal coffee contains no sugar. Lattes contain no added sugar. Milky coffee contains lactose, because, well, it's milky, and that's what latte is.
Now, toffee syrup sugar nut egg nog super large latte with marshmallows contains loads of sugar, but look at the ingredients. If you order a sweet, sugary drink, of course it has loads of sugar in it. I really don't see why this is a shock to anyone, least of all diabetics! If you don't want a sugary drink, just don't order one. They aren't forcing it down your throat!