You don't buy enterprise gear because it's economical for bulk number-crunching... You buy enterprise gear when you have a critical SPOF application (typically the database) that has to be super-reliable, or that requires greater resources than you can get in commodity boxes.
RAS is an expensive proposition. Commodity servers often don't have it, or have much less of it than enterprise gear. Proprietary Unix systems offered RAS as a major selling point. IBM mainframes still have a strong market today.
It wasn't until the late 2000's when x86 went to 64-bit, so if your application wanted to gobble more than 2GB/4GB of RAM, you had to go with something proprietary.
It was even more recently that the world collectively put a huge amount of effort in, and figured out how to parallelize a large amount of number-crunching problems that were previously limited to single-threaded.
There have been many situations like these through the history of computing... Going commodity is always cheaper, but if you have needs commodity systems don't meet, you pay the premium for proprietary systems that do.