I mean we're on the sixth "party system" in the US too, if that's your standard (it's a new "party system" when there's a significant realignment of which interests find themselves in which parties, either by a reshuffle among existing parties, or by new parties rising and old ones falling). Have you heard much about the Federalists or Whigs lately?
The voting demographics change frequently as well. California has voted to elect more republican presidents than it has democrat ones. It’s voted democrat in the previous 8 elections. In the 10 elections prior to that, 9 times it voted for republican candidates. Texas has also voted for more democrat presidential candidates than republican ones. People who think the US democracy is a rigid and highly predictable system simply have a recency bias.
