Any time someone loses value, someone else gains it (in the short term), short of destruction of physical or knowledge capital (i.e. WWII bombing raids). We mark things in dollars but real value is measured in resources, physical capital, and intangible capital (rather than USD). Unless any of that was lost, the $ value losses just re-accrue to someone else instead.
This is different from imaginary value inflating and disappearing (i.e. tokens that never had liquidity - where mark to market never made sense, etc). In that case the whole thing is a mirage.
But if $8 billion dollars went into FTX, that money does not just "disappear" from depreciation - someone else's (or many people's) purchasing power increased in relative terms proportional to the losses suffered by FTX's creditors/depositors.
