Why level 70 - 79 are so expensive ?

[Jojoya]

So level level 62 items you can for 12 k gil . Item that are over level 70 cost over 40k minumum while item at max level can cost 10 k. Can someone give any hint on this topic ?
Any info would welcomed.
Thanks,

TL : DR - supply and demand.

Marketboard prices vary widely because it's a free market. Players can set what prices they want for what they sell. Most sellers are keeping in mind the amounts of gil players already into end game have, not the amount of gil that new characters have. Items in higher demand but lower supply tend to end up selling for more. Items with high supply but low demand tend to get undercut into oblivion as sellers try to unload the items so they at least get something for the item.

Things contributing to supply: crafters, quest rewards and quick ventures.

Things contributing to demand: gear (ilvl) progression being highly valued, players leveling jobs, not having sufficient MSQ progression to be able to purchase tomestone gear appropriate to their level and/or not having access to a vendor selling gear for their level.

Level 62 gear (i265) tends to be cheap because players tend to want to buy new gear as soon as they hit 60 (most see it as a milestone to celebrate). Level 60 tomestone gear (i270) is better if the player has access. If they don't, then it's the crafted level 60 gear (i255) that they get. Considering how much they just spent on the level 60 gear and the relatively small stat increase on the 62 gear, they tend to skip using level 62 gear. The supply builds up on the MB.

Level 70+ gear remains high in value due to demand. It's not uncommon for players to hit level 70 long before they finish the 4.0 MSQ so the marketboard ends up the only source for gear progression until they complete the 5.0 MSQ. That keep demand and prices higher.

Some max level gear is cheap because max level gear comes in tiers released over the end game patch cycles. We've got 3 tiers for level 80: Facet (i450), Neo-Ishgardian (i480) and Exarchic (i510). Gear progression says get the best you can afford so there's more demand for the Exarchic than the other two, lowering the prices on the latter. While all 3 are crafted, Facet and Neo-Ishgardian also come from quick ventures and that increases their supply even more. More supply + less demand = lower prices.