Well no cause as I said they could have showed the ship slowly falling apart and being patched up with alien tec. As well as replaceing dead crew with some delta quadrent recruits as th series went along.
"No support" is part of the premise. That means once something is broken, it's broken for good. No repairs or replacements.
Dont know why voyager would have lost rateing if they had shown a ship falling apart.
DS9 was a war story, yet the station was always totally repaired and the Defiant always in 100% good shape despite constant battles.
As for killing off major crew? How can I buy a situation dangrous or develop a sense of suspence when I know that everything will turn out ok at the end of every episode?
Might as well ask why TOS, TNG and DS9 barely killed anyone.