You have to understand that it's not only curiosity : it's a justification of work that will probably be requested. Put yourself in the devs shoes : increasing the cap requires to put a guy on it. When the team manager will ask why, PR will answer : "dunno, he just stores it without any use" ? Well if I'm the team manager I see it as a non backed request and advise you to spend the gils to make room so you can continue your gil-making activities.

What I agree with though, is that the reason behind only concerns the devs and you, not us on the thread.

On a more personal stand point, cause I'm still curious : if you capped, it means you're not using it. Why want more then ? And in the mean time the devs take to evaluate your request, you could always buy expensive stuff and start auctions or something if you're into roleplay :P