I think it must have to do with zoning or something? There are very few awnings anywhere in Cambridge. I know the owner of a shop who had to remove their custom signage because the building said it stuck too far out over the sidewalk.

Edit: OK in searching, I found Cardullo's application for its awning, which has been there forever. Looks like you need to jump through a lot of hoops for anything sticking out more than 6 inches. https://www2.cambridgema.gov/CityOfCambridge_Content/documents/121203%20app%201%20cardullo%20awning.pdf

Edit2: And it looks like the City Council itself has to vote on approvals. So that's a high bar. https://www.cambridgema.gov/~/media/Files/inspectionalservicesdepartment/OnlineForms/projectingsigndirectionsapplication.pdf