There is reasoning that supports that they haven't actually changed. The democratic party was a corrupt party in the early days of America, and that still remains the case now. Bullying voters, holding racist ideas, and igniting violence with those who don't agree with them have always been calling cards of the democratic party.
I think it is because in general, opinions of people change over time as new things happen. For example, the explosion of gender orientations is a very recent phenomenon. Most people were originally unaccepting of it, but now, in a short time, many people approve it.
