If I were to make a guess, I would say that the Heritage Foundation thinks that all funding of GotV efforts are bad and should be illegal. They are not really fans of enfranchisement beyond the elite they serve. While Republicans have money, it is a commonly held belief that almost all increases in participation by infrequent voters (or eligible but unregistered voters) tends to favor the Democratic party. If the benefit goes to the other party then there is no reason for Republicans to spend in this particular area.