John Gill Commentary Leviticus 18:27

"(for all these abominations have the men of the land done, that were before you, and the land is defiled);" — Leviticus 18:27 (ASV)

For all these abominations have the men of the land done
The then present inhabitants of Canaan, who dwelt in it before the Israelites came into it; these were guilty of unclean copulations, of incestuous, marriages, of fornication and adultery, and of bestiality and idolatry: which [were] before you ;
lived in the land before them, had long dwelt there, but now about to be cast out for their sins; and therefore they who were going to succeed them should take warning by them, lest, committing the same sins, they should be cast out likewise: and the land is defiled; (See Gill on Leviticus 18:25).