Hi, d20games. Great question!
Unfortunately, it looks like you’re seeing a limitation in the Eventbrite API where it limits the length of descriptions that can be passed to it when creating events. We’ve talked to them about the possibility of changing this, but without much traction thus far.
The upshot is that it’s not possible to create an event with a long description/body in TEC and have it work in Eventbrite. If you find this frustrating (which we sure do!), it would be great if you would get in touch with their support team and let them know. They seem to respond more quickly to customer feedback than request from us. 🙂
Sorry I don’t have better news for you!