Treasury Notes were able to be duplicated, and were in huge amounts. So including Smiley, that would be a stockpile of roughly 17,200 gold bullion in 90 days for a duper, and it would require zero effort.
Imagine if a duper took a gamble and did this on three characters for 6 months using duped Treasury Notes and Handmade Presents. That's about 100k gold bullion stockpiles. This ruins any and all possibility of ever adding tradeable items of any kind that could be purchased with gold bullion. In-game equivalent of hyper-inflation. They just added Gold Bullion under the premise of "starting a new economy" like the Federal Reserve, and surely this is a long-term idea that will last into future content.
Now with a capped limit, they limit the damages. Now and into the future. Do you see where I'm coming from?