Yeah, that does seem like it would be a big reason.

On the other hand, a lot of companies might want their employees to have DEI training, and know that those who volunteer are the least likely to need it, but not have any other good way to select people to whom it is novel. That means the trainers need to either be incredibly engaging or accept that a lot of people are simply going to be bored. So if you can tolerate a fair bit of (1) I think you can provide a better service for companies and reach more people.