I've been a developer working for large corporations for the past 4 who are more concerned with "fast" delivery than "correct" delivery. As a result of that, the concept of Unit Testing is somewhat foreign in the environment (I think we have somewhere around 40% test coverage, our unit test suite takes ~40 minutes to run on a dev machine, and new unit tests rarely get written). Unit tests aren't "valuable" to the customer, so they are pushed out in favor of "value" code (features) and the reliance on manual QA testers to catch defects (which doesn't happen).
Imagine you were hired as a consultant to come in here and fix our process. How would you sell TDD to the bosses/managers who only see it as extra work for the same value? I'll admit I'm a little fuzzy on the benefits as well. I'm slightly ashamed to admit that even on my side projects I'm like "I'm totally gonna do TDD you guys!" but that rapidly falls by the wayside.