John Gill Commentary Exodus 8:32

"And Pharaoh hardened his heart this time also, and he did not let the people go." — Exodus 8:32 (ASV)

And Pharaoh hardened his heart at this time also As he did before, when he found the plague was removed, and the flies were gone: neither would he let the people go ; through pride and covetousness, being loath to have the number of those under his dominion so much diminished, and to lose so large a branch of his revenues arising from the labour of these people.