Why Are There Dateless Buffalo Nickels?

By GovMint :

Dateless Buffalo Nickels occur primarily due to the coin's design and wear and tear over time. In this series, the date was placed in a high-relief area that was prone to wear, on the shoulder of the Native American featured on the obverse. Over the years, this date can become worn away from being bumped and rubbed during circulation, ultimately leaving the coin without a visible date.

Sources Used:

https://www.thesprucecrafts.com/no-date-buffalo-nickel-768849