I wonder how much extra it would cost per seat for an airline to cater to those who want more space but don’t care about the amenities of first class. I have to believe that if people were willing to pay more money for more space that airlines would start servicing that market. My suspicion is that in general people are not willing to pay the cost of accommodating their body sizes or desire to use a laptop and they would rather take the cheap fare and try to force others to accommodate them.
Some airlines do. They have economy and a more space economy which has a little more pitch and width. It isn't great, but every inch counts.