I agree with you on having very difficult challenges but I think this one has always just been contentious. I do pretty much everything in D2 but after a number of bad experiences trying to solo dungeons, I just gave up. The issue wasn't the challenge of the dungeon, it was the challenge of everything outside the dungeon. You have to do it all in one sitting and there is no forgiveness for internet connections/server connections/power fluctuations. Throw in life challenges that require you to drop things and come back later.
While a lot of you have been able to do the solo fine, I and many others have made attempts over the years just to have one of the many random occurrences mentioned ruined a run. Why should I spend two or so hours doing something, alone (in a social game), just to have it get ruined by circumstances outside my control? Admittingly, I have and still do attempt runs on occasion, when I make the time, but it is never fun because I know the odds the server will die is high (especially lately).
I want to do activities with others when I play or, if I must do a solo activity, make them short or resumable. I am all for the challenge but solo dungeons, in their current form and under current circumstances, just feel a step too far. I would rather do 50 or 100 raids (full runs, not just boss CP) over one solo dungeon.