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)

How this can be solved ?