The further down this list we go, the more you'll notice that some of the items on it are connected. If Millennial people aren't buying starter homes, and are generally leaving it later in life to buy houses at all, that's obviously going to impact sales at home improvement stores. People can't pay for home improvements if they don't own a home to improve!
At the moment, the disinterest in home improvements among young people is being balanced out by older generations being more interested in the practice than ever before. The over 50s are spending big money on improving their existing assets, but if the young don't engage with the same practice soon, though, their existing customer base is likely to start disappearing within the next decade. They'll probably be hoping that someone has found a way to fix the housing market by then.