Houston is the fastest-growing city in America, but what's really remarkable about Houston is that it's not just Houston. The Dallas, San Antonio, and Austin metro areas are all also growing super-fast and so are several of Texas' smaller metro areas. There are many factors inspiring this population growth, but as you can see above one striking thing is simply that Texas is handing out building permits at a rapid clip (data here).
It used to be that California led the nation in building permits. That makes sense. Even though California's not as geographically expansive as Texas it is extremely large. And a whole bunch of factors would lead you to assume that California would add people more rapidly than Texas. They share proximity to Mexico, but California is home to our Pacific Ocean ports and certainly trade with Asia has exploded. What's more, California has better weather than Texas and substantially higher wages. But in the nineties California downshifted its permitting and ran neck-in-neck with Texas for a while. Then starting in the mid-aughts Texas has just gobbled up a bigger and bigger share of America's permitting. The precise legal and economic underpinnings of this are complicated, but the key difference to me is simply a different mentality. Texas politicians of both parties by and large want to see growth. They brag about it. California politicians fear it, as if we're one new building away from dystopia.
And yet though California is certainly more crowded than Texas, it has less than one fifth the population density of New Jersey and a little bit more than half that of Delaware. Considering that unlike those states, California contains the urban cores of several major cities that's still plenty of room for lots of suburban housing and parks and such. But the state would have to want to see growth.