A year of round numbered anniversaries. It was the 200th anniversary of the nation and the 100th anniversary of the first pro team, the 1876 Red Stockings.
The ATAS was the last of a run of truly epic Topps specialty series that started in 1973 with the all-time leaders cards, then went to the Aaron specials in 1974, then the MVP cards in 1975. I absolutely went nuts for these series as an 8–11-year-old boy. The first Ruth, Cobb, Gehrig, Mantle, Johnson, etc. cards I ever owned were from one of these Topps series. They are still among my favorites.
There were also a bunch of nostalgia series coming into the hobby at the time. From a collecting perspective, the mid to late 1970s was an incredibly fecund era. Everyone seemed to be issuing a card set. Many are documented, others are barely understood.
