Probably the city was feeling time pressure on the whole project, which made them resistant to a new "unproven" concept. We've found them to be incredibly risk adverse - a poor "proven" design is superior to a better idea on many issues.
They basically said it was a good idea, but blew it off. The actual reasons given were:
Effectiveness - concerns about the validity of the technical data on the website. A concern about wood not being as effective as concrete and masonary (they they missed the fact that the soundwall design in the the brochure is actually made of soil, with the willow on the outside).
I don't think they saw these:
http://www.thelivingwall.holz-scholbeck.de/brochures/brochure_ENGLISH.pdf
http://www.thelivingwall.holz-scholbeck.de/brochures/Technical_information_SOUND_BARRIER.pdf
Salt susceptibility of the plants. Street spray - they didn't see any data on this on the website. They did admit, however that this would be a bigger problem for Toronto than us.
Ability to repair/replant after collisions. A good point for soundwalls, but a golf course should have the resources to fix a hedge/or visual screen quickly. Lately I've seen numberous unrepaired soundwalls thoughout the city, so I'm not sure repairing has been a priority.