That's a fair question, and I think you are right that I am making a couple of assumptions in my thinking that you don't subscribe to, which are: (1) that there is indeed a lactate threshold pace at which waste products start accumulating appreciably faster than they can clear, and (2) that running at that pace will result in an adaptation such that you will become better at clearing those waste products at that pace.
Certainly those waste products build up at faster paces, and they build up at slower paces, but trying to find the slowest pace at which they appreciably build would, in theory, allow you to work on that adaptation in a meaningful way with relatively low stress on your body.
And I get that many will react to that with: why are you so focused on one specific adaptation instead of shooting for a range of adaptations across a range of paces? My answer is that this one is one that specifically tries to address one of the generally accepted limiting factors in athletic performance; so it is at least as good a benchmark as any.
For what it is worth, I tend to use the VDOT tables as a starting point for my paces, but do not adhere to them blindly. We all have different inherent capabilities and while the tables are a great resource and guideline, it is unlikely that two runners will have the exact same vo2max/threshold/running economy profile even if they are running the same times in races. Most experienced runners recognize that.