If there’s anything in the Constitution or in the record of the debates at the Constitutional Convention that in any way suggests that apportioning electors from a State in proportion to that State’s popular vote, or in proportion to the number of Congressional districts where each candidate won the popular vote in the district, I have been unable to find it.
In fact, it seems quite clear that the Framers intened to give the legislature of each State full and non-reviewable power to select Presidential electors in any manner they see fit.
They also had the "Rotten Borough" system, and bribery was common.
Still, Britain's Parliament had set an example of allowing the broadest of representative structures.
That's just one of the reasons the Founders left it to the states to decide the who's and what's.