Reply #5: That didn't take much time ...

[RoyGBiv]

If I'd introduced the influence of "progressivism" and "populism," which are essential but difficult to summarize elements in all this ... THAT would have taken some time. :-)

On reflection, the short answer you need is that Republicans have always been greedy, selfish bastards who are owned, lock, stock and barrel, by corporate interests of varying kinds. Where they appeared benevolent on social policy (as we would define benevolence on this side of the aisle), they generally had a selfish interest underneath the surface that moved them to hold that policy.