Taxonomy via Similarity. They are basically identical to a production aircraft's annual inspection, it's natural to call it by the same name. The only difference is that there's no certification standard (type certificate) to compare it to.
It's also a good short cut. Tell non-homebuilder that your plane is having its "Conditional" inspection, they don't know what you mean. Use the term "annual inspection" and even non-pilots immediately grasp what's going on.
I tend to use the word "annual," unless I'm actually talking to my A&P to set it up. Then I use "Conditional Inspection" so he knows that I KNOW the difference.
Next: Biennial vs. Biannual Flight Review! :-)
Ron Wanttaja