How can exchanges create a RVN liquidity pool?

I'd like to know what circumstances must be met for exchanges such as Binance to create a liquidity poor of two(2) tokens for users to easily swap between.
Lets take RVN for example, if you're on the Lite version of the app, you can't easily swap RVN/BUSD you have to go to the market and create a sell order for the asset. What is stopping RVN for being easily swappable for other coins without having to go to the market?