I can tell by your comment you also have never flown in certain remote areas....
Large parts of the rain forests in Africa are just blank spots on maps more than 100 years old-you simply can not get maps, period...
The camp I was in did not have internet access or electricity for the better part of 3 years.... Then came a generator... Followed by satellite internet...
Of course you get an idea on your power available.... But this is no training environment-if you screw up, you don't get a second chance... So if you miscalculated your power available on the approach, you might end up in the jungle with not enough power to climb out of the area again....... Now what do you do?
This is where those checks come into play.... Although they are called "rules of thumb", checking those things while doing a recce before landing always (always!) gave me the accurate information I needed to make a good judgment.....
It's up to any pilot to do whatever he wants.... I will continue doing those checks for the rest of my flying career...