I wouldn't call it hordes.
California's net migration was down like 300K a year, 300K of 39 million is less than a percentage point.
Florida is the only top 10 net migration states that was top 10 in population density. Most of the states experiencing net migration losses are top of the chain in density. Only other state in top 10 population density that gained population in that time frame was Delaware. Most of the states that gained either were COVID remote work expanded states (lost of people left Mass, NY and PA and moved to neighboring states as you saw states like Maine, Vermont and New Hampshire have gains. When people were given the opportunity to make the same amount of money they could and move elsewhere they took that opportunity to get a better house/more land, etc. in a different state.
Couple that with the aging population (2024 had a record high 6.1 wmillion adults hit retirement age) and people deciding to retire to places with mroe space. I'll give an extreme example. Had a coworker who lived in NH, had a decent plot of land and house, they moved to Montana to be closer to their kids and have much more land.