A lot depends on what you mean by “work.”
This just semantics, surely? I don’t think people literally mean they’re doing hard physical labour every day just to be able to tolerate the sight of their husband, breathe in his general vicinity and resist strangling him with his own tie 😂
What they mean is that living with one person for a long period of time inevitably involves moments where you have to compromise, support each other, forgive each other’s flaws and annoyances (because we all have them!), make sacrifices, communicate rather than descend into pointless arguments, and generally not live your life as though everything is about me, me, me.
That can absolutely feel like “work” at times, because our natural human tendency is to want things to go our way.
The idea that you can just float through a marriage without ever having a cross word, while bluebirds permanently circle around both of your heads, is just a load of Disney bollocks!
All relationships require some degree of investment, effort and willingness to compromise. Whether you call that “work” or “compromise” is largely irrelevant -you’re describing essentially the same thing.