I moved to CO from the bay area a couple of years ago.

I couldn't tell you what created the initial imbalance, but it feels like at this point what sustains it is a simple positive-feedback loop. To generalize, when relatively liberal, educated, wealthy people from the coasts want a different lifestyle (work-life balance, better outdoor access, less density, etc.) they move to CO because that where others like them have moved, which further bolsters that reputation.

From what I know, it's kind of like Austin in that the its reputation as a progressive outpost in TX just attracts more of those people.

How places evolve seem like a kind of an interesting study in how branding can become reality.