Aspects of this might be an unpopular opinion...
I definitely get frustrated with the lack of matching swatches on items that should have matching wood tones, fabrics, etc, as well as the obviously incomplete sets of some furniture items; however, some of the best interior design work doesn't depend on everything being perfectly matchy-matchy. Does it make it harder not having matching pieces? Yes! Does it aggravate and frustrate me to no end at times? Definitely! But does it also push me to develop my skills as an interior designer and rethink how to work different items together? Yes! And honestly, I think some of my best rooms have been ones where I've had to really work hard to figure out how to mix and match non-matching items together in a way that makes sense and works.
That said, as much as I appreciate the challenge of working with non-matching swatches and incomplete sets at times and as much as I like how many of those rooms turn out, I agree that we really should have matching swatches and complete sets in the game. I'd rather challenge myself to not work with matching sets when I feel like it, as opposed to being forced to do so ALL THE TIME!