Americans have long been among the most mobile societies on earth, but it's becoming much more nuanced. Local mobility is collapsing but longer distance moving is still a thing, even if it is a declining thing.
Why care? We care because is mobility is one of the central ways via which Americans discover ... that one another exists. Absent that kind of moving and mixing, people tend to self-segregate into comfort 'hoods, blissfully unaware of anyone unlike themselves, and surprised when they find out such benighted people exist.
The causes? High housing prices and high interest rates are the main drivers, but work-from-home has been a recent accelerant, as was Covid. An aging society has also been important, with older societies tending to be less mobile ones. None of these seems likely to reverse any time soon, and the consequences will be felt for decades.