What does the poet want to suggest by describing the beauty of London in the poem "Composed Upon Westminster Bridge, September 3, 1802"?

Wordsworth is effectively saying that here is a place right at the heart of the city which is as beautiful as anywhere in nature. As with most Romantic poets, Wordsworth derived much inspiration from the natural world. Yet here he is, in the middle of one of the world's biggest cities as the dawn begins to spread, marveling at the unlikely beauty of this urban environment in much the same way that he'd marvel at the beauty of a mountain or waterfall.
To a considerable extent, the beauty of the city is related to the fact that there's no one around. Soon the place will be a heaving mass of humanity, with thousands upon thousands of people going about their business. But until then, it's deathly quiet, a characteristic it shares with a remote mountaintop or distant forest. And it's this tranquility that allows Wordsworth to contemplate the sheer beauty of a scene to which he would otherwise be blind.
https://www.poetryfoundation.org/poems/45514/composed-upon-westminster-bridge-september-3-1802