By looking on coingecko, you can notice a volume declining over the years and I might identified the issue, that could be seen as an iceberg.
Visible level : Spot/Perp/DEX prices
Deep level (not tracked) : crypto-swap exchange, localmonero or atomicswaps
Theres a looot of volume not tracked in the deep level, since a monero user is most likely using these ways (just look the last bad new it was a "nokyc" swap)
For people downvoting, have fun keeping paper monero exchanges deciding of the price, because the actual volume isn't shown. (My own opinion on that topic)