Sure, but how would they get to work if there were no buses? A fraction of them would drive, no? Buses are a net positive.
If none of those people would drive instead, or even if only a couple of them would, then the massive bus is a negative.
And even if all of these people lived in walking distance of where they worked, the places they've now vacated would be occupied with people who may drive, and so forth.
The imaginary world you're supposing does not exist, hence the article we're discussing to begin with.