What have we stopped noticing?
The things we say, do, and accept without thinking twice.
Look closer where it comes from, what it assumes, and the case for keeping it
To use something that already exists as support for your own work, or to be carried along by something else.
The story the word seems to tell is that a pig is involved in the ride. The spelling puts the animal right there at the front, which is why the reading sticks.
The record does not show a pig at the beginning of the word. Piggyback is an alteration of the older pickaback, itself related to earlier forms such as pick pack.
The word has been used for riding on someone's back since the 16th century, but the precise origin of the earlier form is uncertain. Online Etymology Dictionary traces piggyback to earlier forms rather than to pigs.
Nobody is misled in practice, and the word does its job. But the pig sits in the spelling, so anyone who takes it for the origin hears an animal in a word that never had one.