It's still early in the morning when Wordsworth composes his famous lines, so naturally there aren't many people about. And even if there were, it's unlikely he'd mentioned them anyway. Because in the sleepy city, Wordsworth sees something similar to the joys of nature he normally writes about. It's as if he's transposed the natural world, with its living, beating heart, to an urban environment.
The city is not really a congenial place for Wordsworth or his poetry, so the only way he can write about it is if he can treat it like an extension of the countryside. Among other things, this means capturing a moment in the city's life when there's no one around. It's the beating heart of the city that interests Wordsworth here, not the people who live in it.