It would be very useful to have a worldwide auxiliary language, but Esperanto's experience shows that the coordination challenges of picking one and convincing

It would be very useful to have a worldwide auxiliary language, but Esperanto's experience shows that the coordination challenges of picking one and convincing institutions or individuals that it's worth it for them are formidable. People may also resent being told that they have to learn a specific language for many different reasons related to their feelings about that language or the people who speak it. You can see pockets (or wide swaths) of resentment toward many widely-spoken languages. I remember being shocked at the thought that people around the world wouldn't naturally get enthusiastic about Esperanto as a sort of Schelling point and just learn it. But if you think about the practical day-to-day communication dynamics that people confront, they usually have some particular regional or national language that would be especially useful to learn. That benefit is obvious and reliably foreseeable, whereas the benefit of joining in an inchoate humanity-wide auxiliary language project is speculative and at best delayed.