1. [尷尬](https://en.wiktionary.org/wiki/%E5%B0%B7%E5%B0%AC) feels like a pleonasm, for it shares [尢](https://en.wiktionary.org/wiki/%E5%B0%A2#Chinese) as the semantic component. Why wasn't just one character, either 尷 or 尬, used to signify the meaning of 尷尬?
2. How common are such pleonasms? What are the reasons for them?