A lot of Monero is being bought or sold on instant crypto exchanges. But they are not tracked through the price aggregators
That is true, but I think it needs to be improved, maybe with adding few more exchanges as source data.
Centralized exchanges all have fake volume anyway for most of the coins listed there.
Monero has biggest volume on Bisq, Haveno, eXch and other exchanges that are not tracked by coingecko or coinmarketcap.
That's also true. We should work on that, but nobody know how to do it. Instant crypto exchanges can't be tracked as well. I checked a lot of options, coz they don't have a trade in fact, it's just a swap. Lower volume - less people know about Monero