There were of course a variety of reasons that the British Crown decided that they would adopt the territories in the Americas as colonies. One of the main driving forces was commercial and one based on increasing revenue streams. As the British were already maintaining colonies across the world and needed to constantly repair and upgrade their navy and other military capacities, the fresh source of revenue as well as possible manpower was attractive.
They were also looking simply to increase their influence in the world in order to promote trade with their merchants and balance power among the other expansion minded european powers such as France, Spain and Holland. The 13 colonies gave them bases and supply centers for those expansion efforts while also balancing the Spanish expansion into Central and South America.
The reasons for Britain's colonization were imperial dominance, the desire for natural resources, and trade. Spain and Portugal were leading the race for exploration and benefiting greatly from Atlantic Trade. This also coincides with the English Reformation, making Spain and England enemies. To assert their dominance and prove that England had the best Navy, the English attempted to "out explore" and colonize as much of the new world before Spain and Portugal. The lands they colonized were rich in natural resources and proved beneficial to the English. The Atlantic Trade system was flourishing and England refused to be left out, and thus these are the most basic instincts of Britain and their quest for colonization.