Trust in God doesn’t depend on what He does for us so much as what He doesn’t do for us, or at least doesn’t appear to do for us.
“Though He slay me yet will I serve Him” – Job
Saying He is faithful in more often than not a statement of belief rather than saying ‘look what He has done’. Sure. we say it when God shows up, but the goal is to say It when we’re confused, disillusioned, feeling abandoned.
Maybe it’s because this is what trains our wills, to asccept His righteousness via our taking Him at His word, regardless of the circumstances.