I hate to be the one to piss in the punch bowl here, but the only reason that they did this is because it in fact didn't require any spine at all.
Whether or not trans women play women's sports is an issue that has no effect at all on the fortunes of corporations and billionaires, so none of the soft money the Democrats receive has been contingent on them ensuring that trans women were banned, so they were free to oppose it, and did. And that's it.