He did this because that was what made him happy, that was what kept him at peace.
He and Coleridge were the first of the Romantic poets. To understand romanticism, you have to start here.
Their poetry differed from so much in several ways, the first of which was that instead of using poetry to show how clever they were, how their intellect was their greatest gift, they used poetry to show how observant they were, to show that their senses were far greater than their intellect.
Wordsworth composed poems while he and his sister walked, long poems which he would remember and write down when he returned from his walk. They often described the places he saw, the people he met, and the tranquility he encountered from walking, from being in nature.
All poems are love poems, but they are not always about two people in love. Sometimes they're about the relationship a man has with the world around him; that relationship can be qualified only by looking at it through his senses.
This is what having the heart of a poet means. Observing the world around you, taking it all in, every ounce of it that is possible, sometimes being overwhelmed by your senses and allowing that to guide your actions, your motivations, and your livelihood.
And loving it. And questioning it. And turning it over in your mind. And yes, eventually rationalizing it. But living inside your senses, not going numb to the constant barrage of sensory input.
The romantic knows the present moment only, he is able to live in that moment, to slow down his own perception of time and see and hear and feel and taste and smell every molecule of the moment.
To know a beloved is not just to know their little quirks, their living patterns, their profile data, but it is also to know their potential. Everything you are in this moment, I see body language inform me and I feel subtle changes in skin, smell anticipation, hear a slight rise in the timber of voices and know what you are feeling.
Wordsworth's contribution to the romantic sensibility is the zealous devotion to nature and the senses. Your body takes in your enmvironment and is at home in that. Your intellect can't see the forest, hear the crunch of the snow, feel the wind. Your rational thoughts can't taste the air as you breathe it in deep.
Only your senses can do that. Only your senses can open up the Romantic Spirit.
Isn't this why the old romantic moves involve things you can smell and hear and see and taste and touch? To open the rational mind to a set of irrational inputs and overwhelm it so that it is forced to revel in it as a child plays and discovers the world around him.
I would much rather see the world as a sandbox to make discoveries in than as a place to be categorized and replaced into boxes as the pragmatists would have. Some life experiences, particularly the most important, can not be sorted and classified.