Ultimately we are all paid to solve the problems the business needs solved, even if the solution is boring and not 'exciting' or 'cutting edge' tech (which is often). The best people finds excitement and challenge in almost any work and are self-motivated. Sure, as a manager you should try your very best to shield the team from crap work and have a healthy balance, understand their interests and find opportunities that match (even outside your team), but ultimately also work is work and is not always, or even often, possible to have super exciting bleeding edge work that fits everyone's interests. Even harder when people have a very narrow set of interests or they don't even know, they're picky, etc.
> I very rarely tell people what to do, because ultimately, I don't have any power to change what they do.
Are you a manager? you very much should be able to change what they do if you are. If project x comes along with twice the value of the current project someone is working on, you very much should be able to preempt what someone is working on. It's not ideal and we all try to avoid project churn, but it happens and needs to be handled effectively by the manager.
> And they'll respect me, and the project, more if they think they're making the decision instead of me.
I mean, delegation and ownership are fine as a mechanism to boost engagement and career growth, but you can't delegate everything (otherwise what are you doing again?). Also, what's up with the "if they think" wording here. Are they making the decision or not, are you tricking them into thinking they're making the decision?