Like most good ideas, adoption has more to do with organizational path dependence than with the quality of idea.
In most companies that have shipped products, a substantial QA division has been created with a senior level QA head. Testing is the fiefdom of the QA team.
The QA team is unlikely to write unit test code because the company typically doesn't staff the QA team with its heavy duty coders.
The programming team is reluctant to write test code because it creates a conflict with the QA team.
I've been seeing more interest and adoption of Unit Testing in groups where QA hasn't been spun off into a separate job function
