I'd say: Performance-wise for most year 2008 hardware when there were more x86-based PC than 64bit.
SHA512 might be faster for 64bit systems but SHA256 is better for 32bit... Also the bandwidth.
That is true. There is no point in using SHA256 any longer, as SHA512 is faster in 64-bit processors
https://medium.com/@davidtstrauss/stop-using-sha-256-6adbb55c608Even if what you need is 256-bit hash, you can still use the more secure SHA512, and just use the first 256-bits.
But in the end of 2008, when bitcoin was created, SHA256 was a good choise.