Why does Bitcoin use two hash functions (SHA-256 and RIPEMD-160) to create an address? Why do we use 2 hash functions (both SHA and RIPEMD) to create an address? Why not just use one hash function?
RIPEMD was used because it produces the shortest hashes whose uniqueness is still sufficiently assured. This allows Bitcoin addresses to be shorter.

SHA256 is used as well because Bitcoin's use of a hash of a public key might create unique weaknesses due to unexpected interactions between RIPEMD and ECDSA (the public key signature algorithm). Interposing an additional and very different hash operation between RIPEMD and ECDSA makes it almost inconceivable that there might be a way to find address collisions that is significantly easier than brute force trying a large number of secret keys.

Essentially, it was a belt and suspenders approach. Bitcoin had to do something unique and rather than have to hope they got it exactly right, they overdesigned it.