Because, in order for the soul to transmigrate, the previous body's got to be dead, and I'm afraid our little pal here was alive all the time.
"Once a Greech"
Evelyn E. Smith
The Welsh bards tell us that the souls of men transmigrate into the bodies of those animals whose habits and characters they most resemble, till after a circuit of such penitential miseries, they are purified for the celestial presence; for man may be converted into a pig or a wolf, till at length he assumes the inoffensiveness of the dove.
"Curiosities of Literature, Vol. 1 (of 3)"
Isaac D'Israeli
In a son, I shall live again,-transmigrate from this tortured and horrible life of mine; drink back my youth.
"Lucretia, Complete"
Edward Bulwer-Lytton