Word: Inline validation

Definition: The inspection and validation of entered data, typically within a form field, before the user hits the call-to-action button.

Thoughts: When forms are validated in real-time, it allows users to complete them more quickly, with less effort, and with fewer errors. The combination of these three things results in greater overall user satisfaction.

We've all been there! That time when you fill out a long form only to his "submit" and realize you committed an error. But now you are back at the top of the page and must become Indiana Jones to find out where the egregious error is lurking. By the time you eventually find it and resubmit you have most likely committed another error. This time perhaps, the form removed your credit card information after the initial submit and you did not realize this when you went for the second go-around. An aggravated email to the help desk ensues.

Now you think to yourself, if only this form had inline validation and I knew exactly when and where I committed that error in the first place!

Note: I may be overly hostile about this at the current moment because of some personal trouble on the Delta Airlines website as of late... just saying.

Question: Why would a designer choose not to use inline validation within a form web?