There are people with multiple capped gil retainers. There is far too much money out in the economy. These few can control markets at will when they want to. However it would be unfair to simply lower the cap and "oh well.. you guys are SOL" especially since crazy amounts or not, they did (usually) get it all within game mechanics. We need something for these people to spend money on that isn't simply swirling the gil around the population. The game lacks adequate gil sinks. Housing is a one time purchase. Repairs are laughable. Teleportation is a extremely minor cost. We used to have things like failing regular melding or difficult crafts to take things out of circulation but all those got turned wayyy down.
We need sinks that work for "endgame" people. We need to take some money out of the economy permanently. For many gil is meaningless. They can buy ANYTHING on the AH without even blinking. I used to be one of those who looked at the housing prices and thought "damn.. that's like.. all the money I've ever made". Not so much anymore. Everything I do endgame brings in millions a week. Treasure maps, retainer ventures, reselling GC seal items just to eat poetics, selling Materia from expert runs, the list goes on and on.
Our economy is broken. There is no regular removal of meaningful amounts of gil.