For me, the best way to attract traders will be the support team of the exchange. We all know that the crypto is congested and sometimes, a transaction can really take a lot of time. A good support team will be a huge magnet for traders especially if they can immediately talk to someone whenever they have issues with their transaction. Wide selection of alts also help attract traders.
I agree with you, being a trader I will look on those exchanges that has a accommodating technical supports that are available 24/7. We can't be sure that technical problem will arise during our transaction as we can ask them for help before we can be panic.