It’s worth noting that these stats don’t show a difference in moving between cities, but between residences. And if you do look at stats showing moves between counties, those have been fairly flat going back to at least 2005 (I couldn’t find data going back farther).
Which is to say that it seems people find less reason to move from one house to another where they already live than they used to. I expect this is because the difference between your current house and a better house has become substantially more expensive than it used to be, making it harder for people to improve their standard of living over time.
I haven't been able to find great statistics, but you can look at state populations to get an idea. California, as an example, went from ~5 million to ~30 million in a few decades post WWII.
California is a pretty substantial outlier there, not exactly representative of the country as a whole, and even then doesn’t actually need a super high inter-state immigration rate to get those numbers. It’s worth noting that the entire country grew 2X larger during those 5 decades. So we’re looking at a 3X increase compared to the average. Which is a lot! But even ignoring the effect of people moving there in the early decades themselves having children that speed up the process…to get a 3X growth over 50 years requires an annual immigration rate of 2.2%. Which would be in 1980, .29% of the US’s population moving to California.
(And as a side note, the above numbers are ignoring immigration. In 1980 California was 15% foreign born people, about 2.5X times the national average. And people who immigrated in 1940s-1960s would themselves have children that lowered the needed inter-state moves even more)
Point is, 5 decades is a long time, only takes a small percent a year to compound. California, by far the most popular state to move to in the country historically, still doesn’t need that high a percent change to get from 5 to 30 million.
Sure, but the point of the rest of those words was to show that to get a 20 million surplus over 5 decades requires, at absolute maximum, .3% of the US to move to California per year in that time frame. (Or more accurately .3% more of the population moving to than moving away from California)
Which is to say that it seems people find less reason to move from one house to another where they already live than they used to. I expect this is because the difference between your current house and a better house has become substantially more expensive than it used to be, making it harder for people to improve their standard of living over time.