They need reassurance that there is no malicious intent within the smart contracts and that the platform is secure without vulnerabilities that could be exploited by hackers. It is important to know the individuals behind the project, the team that is building it, and the community of users.
This is the main issue with dex wallets that they often get hacked. Maiar, Merlin, Dexible, to name a few, were all dex service providers that were hacked in the last 2 years and you're obviously running a wallet, since the money is going back and forth between you and your clients. If other companies that were calling themselves safe because of smart contracts lost their clients money, what would make us trust you?