This allowed them to (a) not run a power wire to every door; (b) use a long (12 digits) passcode; (c) reprogram passcodes in a few seconds; (d) immediately give feedback on whether you had typed in the right code or not.
IIRC they cost upwards of $500 each. Given that there was already a 24/7 human guard to check you in and out, I'm not sure that they made a smart decision over physical metal keys.
Meanwhile, I have a non-networked, non-wireless electronic combo lock on the front door of my house. It's not hackable without physical contact; if you want to break in, smashing a window is a better route. It's powered by a 9-volt battery and lasts about 4 years per battery.
The big win is never forgetting to carry a key, with a smaller bonus of being able to give friends individually revocable passcodes.
Of course the average "smart" lock is unlikely to be engineered with such considerations in mind and I doubt that the extra effort would pay off financially, but it isn't completely impossible.