It was really the Wild West when the original Bourne shell was made, and Stephen R. Bourne was a big ALGOL fan, which influenced the language. In fact, he was such a fan that he abused macros to turn the C source into an ALGOL-like DSL:

https://research.swtch.com/shmacro

https://www.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/sh