It seems like the party itself wants modernize its values, however its the people/ voters who are unwilling to budge. Its like everyone is trying to "out conservative" each other.
Let's not be too kind to the Republican Party itself.
While professional Republicans are probably less racist, sexist and homophobic than the typical voter, the GOP elites are just fine with extremely backward social policy.
The way it works is that the ultimate goal of the GOP establishment is laissez-faire economics (that and subsidies for big business, they love socialism when it goes to rich people). However, most people, even GOP voters really do not care that much about lower capital gains taxes, preserving the carried interest loop hole, gutting social security and cutting the estate tax down to zero. As a result, the GOP establishment must campaign on culture war issues.
So while the GOP establishment is not as racist as Trump and his supporters, they are perfectly fine with indulging the worst instincts of their base all so they can win elections and cut their own taxes and the taxes on their extremely wealthy donors.