But you're not married to my spouse. What reasons would there be for you to declutter? Look at some of the factors that have stirred the "small house movement."
The small house movement (also known as the "tiny house movement") could have early roots in Henry David Thoreau, whose book Walden; or, a Life in the Woods, published in 1854, talked about getting back to the simpler life. For him that involved building a small cabin, with just the necessities.
Where Walden's experiment was rooted in spiritual and philosophical aspirations, the current trend seems to have risen to address the need to find a way to live in an increasingly crowded world, though the need for simplification in a complex life is a strong motive, too.
Let me say here that I don't think I'm a candidate for a small house, for many reasons. Even if I pare down my books to the bare minimum, and find homes for things I no longer use, I have too many different interests to fit in one room.
But I am a candidate for a cheaper house. Eventually I'll want to retire, or at least go part time on the day job. I'll have a lot more choices if I can fit into a smaller house. It will be a lot easier for me to sort things and disperse them (notice I didn't say dispose of them) now. Moving will be cheaper; I can't expect friends to move me, so I need to consider how expensive hiring movers (at least for the heavy items) will be. Having fewer items should decrease the cost.
So think about that. What do you really want to do in life? Do you want to get out of the rat race and follow your passion someday? That goal will be a lot more reachable if you can exist on less money. You can exist on less money in a smaller house, or if you take up less space in a larger, shared house. Either way, you need to have fewer things.
A more-recent incitement for me to declutter was wanting to be the person who actually goes through my stuff. After all, we can't take it with us, though maybe someone could start a modern grave goods trend where your survivors rent a front loader and just dump your possessions in over your coffin... (Let's face it, some of our possessions probably won't burn safely, so I can't see the crematorium going for it. It would have to be an option only for burials and mausoleums.)
I don't regret having gone Big -- it's been wonderful -- but it's not sustainable forever. I'm downsizing, and I'm embracing the journey.
Wikipedia's page on the small house movement:
Tumbleweed Houses, the web site my niece showed me when I didn't understand what she meant when she talked about the small house movement:
Real Simple, a magazine you might find inspirational