That actually explains a lot. I thought that the dense macro footprint alone is why every carrier in NYC seemed to be relying pretty much exclusively on macros for mmWave but now it makes much more sense.
IIRC, NYC regulations lead to a pretty restricted DAS network - thus lots of hardware limitations. You go to any other major city and you'll see multi-sector small cells with higher-order MIMO. Here we're stuck with 2x2 MIMO omni-directional nodes (with the Transit Wireless system being even more limited).
AFAIK, mmWave isn't compatible with the current oDAS hardware. LAA likely fell under the umbrella of "relatively close to what we're already broadcasting", and that's why they were able to deploy.