Who wants a bland white wall?
Hang some shit on that wall. Paintings. Photographs. Random yard sale taxidermy.
Modern styles can still have plenty of personality. Yes, one of the modern trends is minimalism, but that’s not the only modern trend, and there are plenty of ways to explore your own sense of style within a modern sensibility.
I like having a house with really, really good insulation, with good plumbing and electrical up to 21st century fire/safety standards. I like having ducts for my central heat pump and air conditioning.
I can fill in the appearance and style stuff after that on my own.
More accurately, we believe with high probability that it exists because our observations show that the rotation of stars in galaxies don’t behave consistently with the amount of visible matter we can see, assuming that we’ve correctly calculated the universal gravitational constant (from observations of the solar system), that it’s actually a universal constant, and that general relativity is correct.
Maybe there’s another explanation. But dark matter fits really, really well with the rest of our observations, without breaking everything else we believe we know.