tl;dr: don't blame the design, somebody did a crummy job of building it.

Though the real money is in the conclusion:

  Perhaps we should not have worked for a fee so low that it allowed the client to sidestep the usual procedures. Perhaps when we were pushed out of the construction process we could have stepped out because we couldn't guarantee the project’s quality. This is certainly our greatest sin: we should have ended our participation precisely at that moment.

That makes sense. The project they designed would need extensive landscaping maintenance, and can't be done on the cheap.

Though I gotta say, they were picked because they'd apparently done a bang-up job on a project in Rotterdamn that doesn't look all that interesting to me. The scaffolding makes it look like it's under construction. Still, somebody liked it, and it's unclear why they went from a similar design to a "mound".