re: What Caused the Trading Card Market to Bust?

Yep. There was just Topps from the mid-1950s through 1980.

Donruss and Fleer entered the market in 1981. I remember them coming out with Score in 1988 and Upper Deck and Bowman in 1989. Then Topps switched to the Series 1 and Series 2 crap in 1993.

Other problem was that kids in the 1950s and 1960s never kept their cards. They stuck them in the spokes of their bikes, their moms threw out their collections, etc. Then everyone learned in the 1980s and didn't throw away their cards.