Forget Alex & HMPs -_- I tried to point that out, thats not any part of importance. I tried to show that with requoting what I said, and Ill once again, and again I have removed the part about Alex or HMPs.

Problem is someone in the world needs to get items in order for them to be sold. If I have 10 billion gil it matters nothing when no one is farming Flame Geodes. In other words, someone has to farm them, even if I have the money, so why is it the farming cant be done in a reasonable manner so that I can actually spend my money on them?
Buying them is only possible so long as another player obtains them and is willing to sell them. The problem is in the rarity of the required weather or day, thats 1 time every 8 hours or so for day and weather is very random, mostly only during 1 time of the in game year, which is really 1 time of the real life week.

Now to explain what I mean about something being "unable to be farmed" I mean that there is no reliable way to farm them, I could sit in Altepa for 6 hours and see not 1 fire weather, I could see 5 spits of weather 1 minute each, or I could see 1 weather that lasts for 40 minutes without going away, there is no real way of telling. The day has a low drop rate, I normally see 1~3 on most days, with 5 at most on lucky days, this is a very low rate of dropping, and not a reliable way to make money or farm them, so many players will probably avoid it, meaning there is lower supply for buyers and fewer people farming them for themselves.