Learning composing and arranging. Also about chord progression. I know one chord can lead or sometimes has to lead to a specific chord, like I > IV > V > I. Got that. But now had a look at "Eleanor Rigby" from the Beatles. Excellent song from an excellent composer. But to my surprise it has only a IV chord and a vi chord. So no root chord, no dominant chord and a not recommended chord progression (IV > vi).

What am I missing? I know there are no strict rules, but this is so way of from what I thought it would be.