If it took effect right away, then yeah, they'd have given away their vote.  Instead, this only takes effect if enough states to hold an overwhelming number of electoral college votes also pass the same law. It means that New Mexican citizens would have the same voting effect as someone anywhere else in the US - INSTEAD OF HAVING THEIR VOTES EFFECTIVELY WEIGHTED MORE HEAVILY.  So they're giving up an advantage. The reason the electoral college system was set up in the first place was to prevent highly populated areas from dictating to the rest of the country.  This law short-circuits that protection.