To be introduced on (at least the major ones) exchanges costs ridiculous amounts of money. It's coming to the point where it's borderline extortion. Byteball has chosen to be present on a handful of exchanges and instead focus their undistributed funds on adoption rather than speculation. The World Community Grid project is a great example on how Byteball focuses on giving funds to as many people as possible instead of stuffing it into the pockets of large exchanges. If (when!) Byteball becomes big and more and more ICOs rely on the Byteball platform, I think it will eventually lead to larger exchanges listing it simply since they won't miss out on an opportunity to earn money.
At the moment, Byteball's listed on these exchanges:
Bittrex, Cryptox.pl, Changelly, Kaiserex, Biscq, Cryptopia and Indacoin.
Apart from that, Byteball actually has an in-wallet fiat on-ramp making it more convenient for new users to obtain Bytes.