S3 multi-part default setting

[czmrand]

The default multi-partition chunk size is currently 8 MB.
AWS appears to recommend multi-part (upload) for files that are greater than 100 MB.
For larger files, this would decrease the cost of the S3 API calls considerably (~12X).
What is the reasoning behind setting the default to 8 MB (rather than e.g., 100 MB per AWS recommendation)?
Are there any samples you can share that demonstrates the value of this?
(See e.g., here.)