You have just answered the question that is bothering you. The demand for XMR is significantly higher than the offer on eXch precisely because you cannot buy XMR on a large number of other exchanges. I assume that from this you can conclude why there is a greater demand at eXch for buying XMR, and not at Binance, for example.
You want to have XMR in your wallet, and you mention Binance and exchanges where withdrawal is stopped as an example. 

How many truly no-kyc exchanges have an unlimited amount of XMR to withdraw?