Sure, it's ultimately the public's fault. Party power brokers still influence candidate selection, but no longer actually control it. Donors and media influence it, but AOCs still sometimes succeed. In the end, primary voters choose the nominees. Don't like that the primary voters chose a centrist? Then work *within* that party to influence things differently next time (but ultimately it'll still be the voters' choice).
As Churchill said: democracy is the worst possible form of government, except for all the rest.