They then say they will pay a bit more for increased comfort, a couple of inches more leg room and a better quality meal.
'A bit more' would be fine. But as usual the airlines aren't interested in a bit more, they want it all.
BA online one-way fares per seat for the Gatwick - Orlando service, May
2017. Typical for a family heading to Disney, for example:
Economy: £1298
Premium Economy: £1800
That's 40% more per seat, per sector. Is there 40% more space? No.
Let's expand that request to two adults and two children, still one-way:
Economy: £5,045.28
Premium Economy: £7,199.28
Obviously five grand one way isn't sufficient to ensure comfort, the airline needs another two grand to consider offering that.