Geothermal Energy Question- Why do EGS fail after 20-30 years

"EGS (Enhanced Geothermal Systems) wells are expected to have a useful life of 20 to 30 years before the outflow temperature drops about 10 c (18 f) and the well becomes uneconomic." Wikipedia
I do not understand why the out flow template drops, can anyone explain?

If you are removing heat at a rate faster than it can replenish, the temperature of the well will drop. At some point the system will become ineffective.
At that time a deeper well into hotter rock may solve the problem. If the area has a lot of geothermal activity, such as Yellowstone or Iceland, the heat would be replenished quickly and the well could last much longer.