Because it seemed a little lame to repeat the same line when there could be couplets:
May time is here, let us dance and let us sing-o
Flowers in bloom and the birds all on the wing-o
Bagpipe plays loudly a merry melody-o
Lasses and lads in a jolly jubilee-o
Birds in the trees all sing gaily in the sun-o
Take hands with me and together we will run-o
Buds on the boughs mean that spring is coming in-o
Sing all who know that the summer will begin-o
Bring in the May and leave flowers on my door-o
Give me but one, love, and I will give you four-o
Kiss me, my dear, in the morning of the May-o
Leave not my arms, but my dear, please will you stay-o?
Play on the grass in the fresh dew of the morn-o
Springtime is come and the world, it is reborn-o.
May time is here, let us dance and let us sing-o
Flowers in bloom and the birds all on the wing-o