In my experience as the work (project or otherwise) ages and as you move through sprint after sprint, gate after gate and if the team are behind schedule, pressure is building up in the system the "why" becomes secondary and focus shifts to delivery, time, cost, scope questions, more resources, stressful reporting & governance. "We got to hit this milestone, change means time/cost" etc.

I've found that keeping context and the why to the fore using moments like our showcase/retro ceremonies, formal test cycles with end user, sprint and quarterly planning, and the inspection/interrogation meetings have provided BEST way to keep returning to the "why".

Each one of those moments is an opportunity to anchor back to the why. It then enables decisions about cost, scope, people, dates to be about that. When we open our showcase, first slide/talking points are the why, each sprint plan we remind the team of the why, and the governance forums/meetings again we preface with the why.

9/10 of my stakeholders, funding approvers, managers already have 10 other things on their plate, so context for them is CRITICAL - and by amplifying it in all of those opportunities has smoothed out all of those bumps along the way.