Big Yellow taxi and Field Below response

In the poems/songs Big Yellow Taxi and Field Below, the songs don't exactly reflect how the poems sound. In Field Below, the mood of the song actually represents what the poem sounds like. In Big Yellow Taxi though, the poem sounds sad and regretful, but the song sounds happy and joyous. When the poems are read, they sound almost the same. Both authors made it sound like something was missing from life, and that they have a huge regret. I find it weird that such a sad poem could be transformed into a happy song.