Why is the little town empty in these lines from verse iv of "ode on a grecian urn" by john keats?

Read the excerpt.

Who are these coming to the sacrifice?

To what green altar, O mysterious priest,

Lead’st thou that heifer lowing at the skies,

And all her silken flanks with garlands dressed?

What little town by river or seashore,

Or mountain-built with peaceful citadel,

Is emptied of this folk, this pious morn?

Why is the little town empty in these lines from Verse IV of “Ode on a Grecian Urn” by John Keats?

The people are all farmers who are tending their cattle in the fields.

The people were sacrificed by priests of conquering armies.

The people have all gone to attend a religious ceremony.

The people have all gone on trips to the seashore or mountains.

if you have to come up with one i would do

love: happiness