To gain trust, a sportsbook must be trusted and can provide unique services which have licenses and certificates. As well as having cooperation with international agents to provide the most complete sportsbook services.
I've heard that it's easy for a new casino to get a license. There are casinos that are new and they don't have the pure intention of providing such service but just trying to collect as much as they can and then will eventually turn into devastation.
It's important to have a license but I don't think that it shall be prioritized anymore and it's more of becoming a requirement that's needed as a business. But not a big factor anymore for someone who looks for a trusted one and the majority is based on the performance of that new casino.