Typical forum response. "It's all money greed on SE's part, they could do it if they wanted to but they just want to milk us for more money".
It's a for-profit business. If you don't like paying businesses who want to make a profit, stick to doing business with non-profit organizations. You might want to think about just how much money you'd personally be earning if Western economies didn't revolve around the for-profit business model.
Why can't you have more inventory space? Because it clogs up communication between server and player clients when inventories are opened and items changed. The more that has to be communicated the slower the servers respond to inquiries in general, whether inventory, chat, combat or just about anything else we do in the game. Because data doesn't take up zero room on the servers, especially when you're multiplying that data by the millions of existing characters whether or not they are currently active. There's a point that SE needs to acquire more server space to accomodate the increased data and that space doesn't come free.
SE does add in more inventory when they can find solutions that ease the communication issue. That's why we have a chocobo saddlebag now.
Why not just leave all inventory information stored solely on the player's local client until the item is removed from their inventory so the need for server-client communication is reduced? Because cheating - imagine if players had free reign to edit their inventories without some sort of authentication from the game servers.
Why are fees charged for extra retainers? Because it makes more sense to only charge those players adding to the problem with their hoarding instead of charging every player, most of whom don't need the additional space.
Believe what you want instead of researching to understand the problem. Your complaints don't make the problems go away. SE will implement improvements as they find solutions to those problems.