why
From LSJ
οὐ γὰρ ἂν τό γε πραχθὲν ἀγένητον θείη → since he cannot make what was done as though it had not come to pass
English > Greek (Woodhouse)
adverb
Interrogative: P. and V. τί, τοῦ χάριν (Dem. 490). P. διὰ τί, τοῦ ἕνεκα (Dem. 1104), ἀντὶ τίνος (Plato, Lysis 208E), V. πρὸς τί, ἀντὶ τοῦ, εἰς τί, τί χρῆμα, τίνος ἕκατι, ἐκ τοῦ (Euripides, Electra 246), τίνος χάριν.
for what purpose: P. and V. ἐπὶ τῷ (Sophocles, Ajax 797).