Yeah, that's exactly what people do already.

And secondly it doesn't take an extremely high temperature to reduce steel's strength. Many steels starts losing strength at 200°C, cast iron at 400°C. Source: https://www.engineeringtoolbox.com/metal-temperature-strengt...

This doesn't mean that the drill is soft but at extreme depth extreme hardness is required.

So why is that not enough?

What would digging even deeper get us?

I don't know. I am afraid that article is bullshit. So it doesn't make sense to give an answer to your question.

This aside, let me give some examples about geothermy. In Iceland and in New Zealand it is possible to get hot water from the ground without deep drillings. In Switzerland there was a failed project about geothermy, because the drill down to the granite bedrock at a depth of about 2700 m and deeper caused an earthquake. People in Basel are very sensitive because it was a location of an huge earthquake 1356.

In other words, we don't need to drill so deep at all. YAGNI.

You need about 500C for steam turbines to be good, and the relatively weak heat won't last.

I guess you could use the heat as you go to try to cool it enough to keep drilling over a few years.

Another idea might be to have solar panels or wind turbines up top and geothermal below. Both could use molten salt storage, from which energy is generated on demand.

This way, any heat generated from geothermal would not be wasted.

It's just a matter of whether the economics of drilling and maintaining the bore hole would be worth it.