I can't speak for the author but I can say that I left companies or institutions on my own despite loving both the (idealized) mission and the team.

I wanted to stay but the strategy was wrong, to my own moral compass.

Consequently leaving in silence, without being able to express why, and maybe even what could possibly be fixed, feels like giving up.

Leaving while telling whomever might want to hear what problems were, and possibly how to fix them, helps to move on while being truthful.