It goes back further. Reagan surrounded himself with Bushies and Country Club pubbies from Day 1. The conservative movement was betrayed and screamed bloody murder, but most of us couldn't understand why. We were blinded by a personality cult and we got used by The Establishment, as always.
I think I understand Reagan’s move. He had run for President in 1976 and lost after he was portrayed as too extreme for the electorate. 1980 was only 16 years after Barry Goldwater lost in a landslide, and the common wisdom was that he lost because he was portrayed as a conservative extremist. Reagan’s likeability came through strongly in his 1980 campaign, but I think he felt that he had to bring in Bush and some of the Country Club Republicans (I regard them as today’s RINOs) in order to close the deal.
He may have been right in 1980; he was too much of a gentleman to dump Bush in 1984, and unfortunately by 1988 I understand that he was fading mentally and not in a position to back another successor.