Lewis Thomas, by the way, may have gotten the idea from Arthur C. Clarke, who emphasized the universal appeal to the intellect of Bach's music in his novel _2001_ back in the 1960's. No idea why Kubrick picked Strauss for the movie version.
The script for the film actually predated the novel. Kubrick used both Strausses and Ligeti.
Whatever the reason, Thus Spake Zarathustra (Richard) and The Blue Danube (Johann) worked brilliantly. Still, it is a bit surprising ole Stanley couldn't find a place for J.S. Bach's music somewhere in the film. ....especially since he worked so closely with A.C. Clarke in its making.
"No idea why Kubrick picked Strauss for the movie version."
I believe the story is Kubrick had already commissioned the famous Alex North to do the music for 2001.
But while he was editing the movie they were playing music (as was their wont) and "Thus Spake" came on, and just seemed to fit perfectly.