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 ?
Even if Monero daily transaction volume seems low compared to cryptocoin X , Y or Z. That’s not a problem
can any other coin (other than bitcoin) point to numerous different marketplaces using monero as standard?
can any other coin offer what monero offers to market participants?
and lastly; numerous sources have researched wash trading - including US Gov, big banks like JPM and each find that at least 70% of transaction volume is wash trading.
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4649565
as such you can look at daily volume and diminish it by at least 70%, then compare.
[not saying there isn’t fuckery with xmr price, especially until binance drops it] [also noting that the question is still valid about how data is collected on transaction volume for xmr in private]