Its all about what you are used to and what your abilities are. I do non stoppers walking continuously for sometimes 35 hours, with maybe two short stops of 20 minutes each for attention to the feet, eating and drinking on the move. I am now 62 years and still doing it and my phylosophy has always been, 'If I can do it so can you, providing you practise as much and as hard as I do, but more than anything - you have to want to do it. I have tried to walk slow, and only ever acheived it when walking with my wife. Carrying a rucsac of 36Ilbs yesterday, I did a 14 mile route near my home to practise for my forthcoming 10 day attempt on the Pennine Way. I just wanted to walk at an average 2 mph, but it seemed so slow and I ended up averaging just over 3mph. Carrying a light sac, some weeks ago I averaged almost 4mph, all walking, round the Yorkshire 3 Peaks route. Its all in the mind set. Obviously if you are wanting to walk long distances, especially when backpacking or doing non stoppers, you have to have the mental strengh and attitude to succeed, and this is developed over years of pushing the limits. A half hearted approach will lead to failure and disappointment.
I am not for a moment suggesting that everyone should walk this way, not at all. I have the utmost respect for everyone enjoying their walking the way they are happy to do so. I am merely putting forward a little explanation from one (me) as to why we, that do walk fast and far, do it, whilst those that dont, see us as rushing it.