"Many of the [system's] details only become known to us as we progress in the [system's] implementation. Some of the things that we learn invalidate our design and we must backtrack."
Top Down doesn't backtrack easily. It's more start over than backtrack, and no one wanted to do that. Imagine painting a family portrait and then having to add another person to it. The IT industry tried to mitigate Parnas' reality by creating RAD (Rapid Application Development). Requirements were gathered and upfront focus groups with critical stakeholders and iterative prototyping were used to drive design and development. This solved most of the backtrack problem, but many IT teams struggled with prototyping that would never end. They called this death spirals.
SAM, created by Allen Interaction, has emerged as an alternative to ADDIE, especially when doing e-learning solutions to drive performance improvement. The kick-off focus group is called Savvy Start and the risk of death spirals has been mitigated through three design and three development iterations. Allen Interaction's philosophy maps the purpose of this methodology toward driving performance. The current iteration of methodology is Agile.