It is true that states are allowed to pick electors however they wish under the Constitution, and that states may enter into interstate compacts on a variety of issues, but they cannot functionally eliminate the Electoral College without either passing an amendment to the Constitution, or by amending the Constitution in a Constitutional Convention. The Constitution explicitly reserves the power to have electoral colleges to the federal government by putting it in the Constitution, and it specifically enumerates how changes are to be made to the Constitution. The Constitution trumps the compact under the federal supremacy clause. Amendments are ratified by going through Congress with super majorities and have to be approved by 38 of the states. For instance, the states can’t have a compact among themselves to no longer send representatives to Congress in order to close down the House of Representatives.