Why William Wordsworth Write London, 1802?

The poem that you are talking about is actually titled ' To Milton' and the subtitle is "london 1802'. In this poem Wordsworth pays a tribute to the genius as well as moral character of Milton and invokes him to come back and save England from the clutches of Industrialism. The theme of the poem is the same as 'The World Is Too Much With Us' but here instead of escaping into paganism Wordsworth wants reform with the help of his model hero of English history. The basic motive behind writing this poem was Wordsworth's sensitivity to the ongoing industrialisation which he felt was decaying the English heritage which he thought was rich with manners, virtue, freedom and power. He believed only Milton could come to the rescue of his countrymen who had turned selfish and materialistic.