Satoshi did this minimization because it is good design sense, it is sufficient security and collision resistance, it provides an extra layer of protection against any unknown cryptanalysis interaction between SHA256 (or RIPE160) alone and ECDSA, and it helps to market the product to the n00bs as scalable (even though Satoshi was deception in this regard) in Bitcoin's nascent stage. Also SHA256 before RIPE160 provides an extra layer of protection against any
unknown cryptanalysis breakage on collisions for RIPE160 alone. For example,
SHA256 has a Merkle-Damgard length extension weakness when not doubled with itself or another hash,
which tangentially btw would provide someone with a strong hint as to where to look for inventing the AsicBoost to make SHA256 mining 30% more efficient.Satoshi was so genius that he designed the AsicBoost into the design.
I can say that with great confidence because double-hashing defeats attacks such as AsicBoost, and Satoshi
did double-hashing as a precaution every where it could be required in his design except for the proof-of-work.
He managed to think far ahead on the game theory and realized he would need a poison pill to ensure that no one could modify his evil design.
So therefor he created a design that he knew the Chinese ASIC manufacturers would figure out how to make covert AsicBoost and that if it was patented outside of China, then this would be the poison pill against any changes to the protocol (as I have recently explained at @gmaxwell's Redditard discussion).
@dinofelis STFU on your nonsense about Satoshi wasn't genius. I've strongly refuted
all of your nonsense technical claims. Stop your lying nonsense.