The "Champagne" airline started well before the SLC hub. Western was focused more around LAX at that time and didn't have a major "hub". Most of the service was point-to-point.

As other airlines invaded Western's west coast, point to point route system, Western was in rather dire financial straits. The SLC hub was more of a "Hail Mary" attempt at reviving the airline. Fortunately, it turned out to be a successful strategy in the West. In the 80's, I remember thinking SLC, really?!? But, other than DEN which had UA, CO, and Frontier, there was no other viable choice.

When airlines were looking for merger partners in the late-80's, Western filled a gaping hole in DL's hub system. The hub at SLC and large operation at LAX fit well with DL's DFW, ATL, and CVG hubs. Arguably, it's western operations have long outlasted the US/PSA and AA/AirCal/(and later) QQ combinations. Only UA's SFO hub has really thrived.