Well, we will not get a proper answer to what the real volume is because they are doing it behind secret doors and nobody really has the answer to it, or any data that can back it up. First of all, not even exchanges knows how much of the volume they have is fake all the time, they do the fake volume themselves for some coins but at the same time they are not doing all of it, they let the coins do it themselves.
We cannot really see it, we can only see through a window of a house whose built is 2 storey. So if ever these exchanges are using some manipulative techniques to catch and attract traders then might as well the authorities should look after them, I just don't know if there are some laws regarding this but this is some kind of fraud.
Binance and some of the other huge ones have specific auto trading bots that basically trade inside the spread so it looks like there is a trade going but in reality someone is buying and selling from themselves and losing some money by doing so to the exchange but it keeps them from getting delisted. Exchanges do not have numbers of those ones and that is why no real one person knows all of the fake ones in any exchange.
This is a serious accusation especially with binance, maybe you are just carried away by a massive traffic on their exchange that made you think that there is a wash trade happening since Binance has millions of users and price movement in there is unlike the others. This is why choosing an exchange is really a priority, you need to know where your money is sleeping every night.