With their massive subscriber growth I'm not surprised, it seems a lot of the network investment they've been pushing has been extending coverage and in-building service with their Band 12 licensing. With them looking at deploying a "5G" network by 2020 I'm not sure if there are plans to add new cells right now, they have plenty of backhaul but the physics of shared RF spectrum is biting them now that they've had so many consecutive quarters of net subscriber adds.

Here's hoping they do invest in some more cells for my dense metro bretheren, because I enjoy 60Mbps at least day-to-day here in Boise :/