Allies strictly control what they share with others, in terms of classified information. Not as much classified information as you'd think is actually five eyes. Most of the stuff collected on foreign allies and axis powers is NOFORN and shared on an operational/strategic basis. Intelligence agencies only share across borders with specific, limited scope frameworks; Biden can't just ask for everything GCHQ and MI6, for example, have collected on Trump. Five eyes is a very specific framework with a specific scope. Everything at the high, foreign relations level falls far outside of the scope of FVEY. Allied powers might willingly share all the intelligence they have, or they might withhold intelligence and sit on it for use later, for strategic reasons.