They are that steep and deep because Slartibartfast thinks they are pretty.
So is a fjord with water in it the same thing as a Scottish loch? I’m not trying to be sarcastic but it does get confusing...I always thought “loch” was Scottish for “lake”, but they’re really, really deep! They look so peaceful when you see them, but I guess that may be where the term “still waters run deep” comes from. I thought a fjord was kind of the same thing...Damn, I dunno, I grew up around bayous and “cricks”!!:-)