we can see the rampant deflation in the value of gold in the graph correlates directly to the TP going up and down.
this graph isn’t perfectly accurate at least in teh first marker wher ethe tp was actually going up and down mor efrequently than the maker suggests.
basically to understand the data here, we must realize that valleys mean you get less gold per 100 gems/dollar.
which in turn means that valleys = spikes in the irl $ value of gold.
there’s a number of factors of why buying gold primarily when the tp is up is attractive-
crafting- the high cost of trophy mats(ie fangs, claws, vials of blood), combined with the high costs of vendor mats(in particular runes of holding, spools of thread, etc) together contirbute to making crafting extremely expensive vs income and drop rates of those items while questing normally(ie not focused entirely on farming the trophies while ignoring high exp activities like hearts adn events) as trophy mats have a very low drop rate compared to how many are needed to progress a non cooking profession anywhere near your combat level.
high cost of money sinks such as the trait teir books, siege weapons for wvw and so on.
low ROI on crafted items, with bags selling lower than they cost to make and stat gear selling typically for vendor price +1c(ie losing money even vs vendoring it), and far far below the value of the mats used to craft them.