I think that geothermal works better in more extreme climates. If you compare it to an air source heat pump, the main advantage of geothermal is that the sink temperature is the ground temperature, which is roughly the average of the temperature over the course of the year. In say, Austin, TX, the difference between the average high in August and January is 35.5degF. In say, Chicago, it's 52.7degF. In Austin, the average temperature is 69degF. In Chicago, it's 52degF.
The Austin average temperature is essentially room temperature, and the deviation is much less, so the total amount of heating/cooling you have to do is much less, so any efficiency advantage is reduced by the smaller need to heat/cool. This compounds with the fact that the average yearly temperature is closer to the outside air temperature, which makes the advantage of the ground source less.
This compounds with the fact that Texas energy prices are some of the lowest in the country, and it makes it a lot harder to justify a big capital expense to reduce these costs.