It's highly unlikely that root causes are only technical

Even in the simplest situations, it is highly unlikely that root causes end up being only technical.  The purpose of pre-defined categories used in Ishikawa diagrams is to remind us to consider multiple avenues of causation.

The traditional categories in manufacturing are the 8Ms:

• Machine
• Method
• Material
• Man
• Measurement
• Management
• Maintenance

However, the categories are not limited to the traditional ones.  For example, I like the Six Sources of Influence for framing behaviour-related problems:

Why didn't Bob use Test-Driven Development (TDD)?

1. Personal Motivation: Bob doesn't enjoy TDD, Bob thinks testing is dead, etc.
2. Personal Ability: Bob doesn't know how to do TDD
3. Social Motivation: The other developers on the team are hostile to TDD
4. Social Ability: Bob has no one to ask for help when he has questions about TDD
5. Structural Motivation: Bob is rewarded based on code produced even if it doesn't work
6. Structural Ability: Unit testing frameworks and libraries are not available for the technology Bob is using

In practice, I still prefer a more brainstorming and affinity grouping approach...

1. Brainstorm potential causes
2. Group the causes by affinity
3. Filter out causes that are unlikely
4. Apply 5 Whys to remaining causes to flesh out the rest of the tree

... but pre-defined categories are useful to seed more ideas.