Group / corporate rates are a tricky thing to ascribe broad strokes to. Some may include less onerous cancellation policies or other benefits that aren't included in the rates you find online making them a better option for the group even if the sticker price appears the same.

For example while our corporate rate is usually cheaper than publicly available rates, even when it's the same or within a couple of dollars, our corporate rate always includes cancellation until 6pm on the same day as arrival, waives any destination fees (e.g., the ridiculous fees that the NYC Marriott's charge), and includes access to the gym regardless of status (where such a perk is relevant).

Plus you never know what deal specifically that group has with the uber chain -- the hotels near our various global offices are ridiculously cheap even in major cities like Tokyo / London / Hong Kong / New York and it's likely due to the volume of stays they see at those locations from our company.