1977 What gives?

What happened to 1977? I do not understand why they would not always have a 70s single season available. I guess demand is not there?

Additionally, I recently saw a 1977 league but I could not find the 1977 set. Any idea what that was about?

Personally, I feel the 70s are a sweet spot for SOM age people. I would love to know why we do not have 77, or whatever 70s year they'd like.

1977 was dropped and 1964 was introduced. They are "limited time" sets. There may have been another year in-between. My group played 1977 in July '22 and we are playing 1964 now.