There’s no compelling reason why a state a big and wealthy as Texas can’t afford to manage natural disasters on this scale.
Their state leadership simply chooses not to do so. And the state media saturated the airwaves with “Nothing to be done, government would only make things worse” which… given the leadership of the state, isn’t even an unfair critique.
Broadly speaking? For the same reason every other state does. Continental unity opens up trade and travel, exploits economies of scale, and simplifies the legal system for interstate business and for civil rights purposes.
Specifically? Because federal coordination helps manage natural disasters (like wildfires) and centralize big programs life Medicare/SS and secures national defense (which California profits from handsomely).