Economic vs Range weapons - Both right.
There was no guarantee that the one peasant with succeed killing a knight with his crossbow before the knight got into range. There is a reasonable level of certainty that 50 peasants (untrained) with crossbows could take down an armored knight. The peasants and crossbows where cheaper by far.
Saying that it was an economic development might be true. One could then ask what started that development. Is it that a crossbow shortened the lives of the fighting nobility and the smart rulers saw the need for change and adapted first appearing to lead the trend? Economics is very reactionary, meaning something else causes change, not economics itself. Medevial society was very, very resistant to change, to the point of actively purging those who were not the norm. Being a man-at-arms and acknowleging crossbows as deadly makes one look at how he can react to it. That man-at-arms does give up his position in court because society would be better served by a different military. Saying because the nobility funded the research does not mean they wanted to give up their positions in court. The changes to society they wrought were done in self interest and self interest alone. As the world view at the time was one where everyone had their place and any change was bad, if Charles the Bold of Burgundy had tried to change society, he would not have been viewed as the most chivalrous, as part of the code of chivalry is to maintain the current order.
Biggest case in point to how reactionary thought had been in the past can be shown with the lack of change in warfare from 1400 to 1900. Even with the rising power of ranged weaponry, troops were always tighly packed. This was exploited in 1400 because peasants were recruited to fire crossbows based on their reload speed, no accuracty (they just pointed in a direction and shot, farthest recorded kill for a crossbow was 5 miles it was a complete luck shot off a tower ontop of a cliff into an advancing army). It took 500 years for people to figure out standing in the middle of a field is a bad idea if people are shooting at you. Yes, this is very simplistic, but the point I am trying to make, the English had a hard time with the French and Native Americans in the mid 1700s because they did not "stand up and fight", and they still hadn't changed their tactics to fight WWI.
I would actually posit that society itself caused the unnecessary extension of the man-at-arms life.