What did they do that required an assumption of intelligent creation?
The general argument that has been in the consciousness of the West (and, it's safe to say, in the minds of the scientists mentioned by the OP) for a long time goes something like so: Creation manifests design and teleology because God is intelligent and He made it so; creation is comprehensible by rational minds; we are made in the image of God, and so we are able to comprehend something of the purpose and design of the world around us. Hence, science. It is interesting to examine the state and history of science in cultures that did not develop these notions about intelligent creation.