Nice punchy logic. If declarer has ♠Ax, partner has ♠T9x, which can theoretically be crushed for three spade tricks (♠A, ♠K, ♠J crush). Then they can hook a club and they're home. But will declarer notice the potential of their ♠6? Probably not. And on the off-chance declarer has upgraded with five clubs, you certainly want to keep the suit guarded.