In chess, why is 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Bxc6 rarely visited?
This is called the "Exchange" Variation of the Ruy Lopez. Not only is there an early exchange of bishop for knight, but it usually soon leads to an exchange of queens on d4.

This queen exchange brings about an early "endgame," effectively cutting out the middle game. Most players are not particularly fond of the endgame, so they don't consider this an advantage, and therefore don't play this variation.

But in a famous game in St. Petersburg in 1914, the world champion, Emmanuel Lasker, played this variation against future world champion Jose R Capablanca---and won. By Capablanca's own admission, "Lasker had no superior in [the endgame]" at the time. On the other hand, he already (and later) feared Capablanca's middle game.