Also, the opposition to prenuptial agreements is multi faceted. Middushin al tanai is discouraged by achronim(maybe even some rishonim) because there are a million….tanayim (pun!) Involved and different opinions as to how to make one work. Playing around with tanoim is a recipe for mamzerim.
The other reason is that including such things is to decide from the get-go that the marriage may be doomed.
Copying the practices of goyim in our marriages is not our way.