The AT&T corporation was massive back then. These folks were looking at rebranding every piece of equipment in the country, it wasn't going to be a cheap adventure. Bass did the right thing by making them comfortable with the cost.
I met a designer at Verizon once, asked what the hell the deal with their logo was. He acknowledged that it was rock-bottom, worst-of-the-worst grade… and said that their own internal studies indicated a multi-billion dollar project just to change all the signs.
Like, just look at that one sign overlooking the east river in NYC. That logo’s gonna be around forever.