If unit testing is so great, why aren't more companies doing it? [closed]

In my experience, there are a couple of factors involved in this:

1. Management doesn't really understand what unit testing really is, or why it has real intrinsic value to them.
2. Management tends to be more concerned with rapid product delivery, and (incorrectly) sees unit testing as counterproductive to that goal.
3. There's a misperception that testing belongs solely in the pervue of QA. Developers are coders, and can't write tests.
4. There's a common misperception that management will have to spend money to do unit testing correctly, despite the fact that the tools are freely available. (There is, of course, the developer ramp up time to consider, but it's not really prohibitive.)
5. Will's answer will round this answer out: It's very hard to determine the value of test code (edit jcollum)

Naturally, there are other factors, but those are just what I've run into so far.

1) It's hard
2) It takes time
3) It's very hard to determine the value of test code

Point 3 is a sticky one. Good unit tests reduce bugs. But so does good production code. How do you determine how many bugs don't exist because of your unit tests? You can't measure what does not exist. You can point to studies, but they don't fit nicely on your business manager's spreadsheet.