You're right, a CTO doesn't usually write software, a CTO manages programmers who write software (or VPs managing teams of programmers, etc). But a CTO generally comes from a coding background, and how much data science do you think a "chief data scientist" is really doing, as opposed to managing other data scientists? People in the C-Suite typically don't really do anything other than manage people managing others in the same background they came from.
I think the spirit of my point still stands, pedantry aside. There clearly exists a commonly used and recognized c-suite role for programmers, whether they use their programming ability hands on or in managing others. It's not at all clear to me that there is a commonly used nor well recognized c-suite role for data scientists that would be distinct from CTO.
As a category of employee and work division, data scientists have not yet become distinct enough from cross-polinated disciplines to have that sort of representation.