I mean....supply and demand...but also, greed. There are probably just way too many people botting on his server for the demand of the market.
Supply and demand is exactly what you need to abuse though.. You let stuff sell out, and if a market is already flooded, don't flood it even more (Help the market empty out), so you can relist for a higher price..
Let's say everyone let the HQ leafborne sand sell out on his serve, and then they all started relisting for 3-400k again, the demand is there.. So they will sell..
I understand market board undercutting and all, because who doesn't want the sale.. but at some point people have to stop and realize that they have let it drop too far.. Even pipira pira.. it's one of the most popular all purpose foods out there.. so the demand is there.. instead of everyone taking advantage of that, people are spamming the food, even after it has dropped to let's say 5-10k when they could be getting way more, I don't know how your market prices are, but if I were to buy all the mats to make pipira, they would be about 4k a piece, so definitely not worth selling for 5-10k..
I realize there's a lot of people botting food like Pipira, but that's still time spent, and time still = gil, even if it is another account. having to spend more and more "time" to make the same amount of gil.
There are still good markets out there, that haven't been heavily invaded yet, which means that even if I do bot it, I can make the same amount of gil in 30 minutes that someone who just floods markets has to use an entire day to do. And that means I can spend the remaining 23 and a half our of the day on numerous other less time consuming things and make even more gil..
Anyways.. That's just a rant I guess.. Everyone would be making more gil in less time if they did it smarter is all..