LMAO
Just keep thinking that to yourself, pal. Maybe someday you'll actually do some research/study and realize how foolish you sound. Your statements have said all we need to know about your "understanding" of economics.
-Signed International Business/Economics double major and owner of two businesses
EDIT: To expound on this.
So before the world visit system, market boards were limited to their own worlds. From an economic perspective, this would be like countries not trading at all with other countries. So each country (world) had it's own price equilibriums
What world visit did is allow you to sell to people from other worlds (countries). What this did/does is bring all worlds closer to a similar price equilibrium. Before, one world might have sold an item for 100,000 gil, but another sold it for only 50,000 gil. Now the price equilibrium has dropped for the item overall.
Since anyone can visit any world, there is no need for the ability to sell on another world, as anyone can come to your world if you've got the most competitive prices.
And the reason they don't allow selling on other worlds is a logistical one, not a design choice. Due to how their retainer system works, that's why you can't sell on other worlds.