While MOST exchanges report fake volume, it doesn't mean the most of the volume is fake, according to study/audit https://www.sec.gov/comments/sr-nysearca-2019-01/srnysearca201901-5164833-183434.pdf , we know that at least the following 10 exchanges provide accurate volume
Binance > 536,016 BTC
Bitfinex >8,556 BTC
Kraken >19,765 BTC
Bitstamp > 12,929 BTC
Coinbase > 26,752 BTC
Bitflyer > 7,079 BTC
Gemini > 1,473 BTC
Itbit > 608.75 BTC
Bittrex > 3,142 BTC
Poloniex >5,089 BTC
Total = 621,410 BTC average last 24 hours volume.
Notice that volume is in BTC not USD, in USD it's about 6 Billion, and this ignores every other exchange ( a few hundreds of them) and based on the assumption that 100% of the other volume is fake, which we all know is not the case, mind you the last 24hrs volume has been pretty low, so in many days we do actually hit 40B probably only out of these 10 exchanges.
Trading volume matters, in fact, ask yourself, if not for Tether and all these exchanges, would bitcoin ever go past $100? certainly not, you can't count on OTC markets and a few nerds exchanging bitcoin for some pizzas and a few perks of certain online games, these global trading platforms are the reason why bitcoin is worth this much, in fact even the majority of bitcoin transactions go throw exchanges, people trade bitcoin more than they actually use it, on the grand scheme of things, the use of bitcoin as a payment method is close to nothing, this is the same thing with gold or any other asset, it gains the most of its the volume from trading, not by sitting in a cold wallet doing nothing, its a sad thing but that's reality, you know it is when a whale places a huge short order of bitcoin he doesn't even own, selling/shorting an imaginary future contract that can take bitcoin 30% down in a few minutes, and the same thing happens on the way up for obvious reasons, long story short, trading volume DOES matter.