Sure, some trust is required that they aren't breaking their own terms of service (which legally enforces that they won't train on your data), but the same is true of every company/service you deal with (AWS, Google, your CRM etc). Their entire business model depends on enterprises trusting them.
But if you're going to take your distrust that far then the issue is that they have your data at all, not that they are telling you that they will retain it for 30 days.
