In places where Geothermal is cheaper than this you will in fact see a lot of Geothermal wells. Geothermal works great in geologically active regions. This option works best in geologically inactive regions. The two options complement each other in my opinion.

Not depending on industry specialists that have to retain talent & tools for a 15 year gap in their order books probably helps competing with complex containment structures. They can buy some fairly premium drill bits and still be the lowest bid, if only they can be trusted to promise more realistic service entry date than contemporary "13 years behind schedule" designs.

Drilling has to be extremely cheap and the geothermal heat extremely high to be economical, which is why it makes sense in iceland but not mainstream.

Drilling and putting a nuclear reactor underground, much shallower than the deepest coal mines, can be quite expensive and still be cheap as a part of the total cost of the nuclear power station?

On average, the Earth's crust is over 10 miles thick. There's a pretty big difference between drilling 1 mile and 10 miles - literally an order of magnitude.

Yet they go for oil at these depths even at the risk of a dry well.