The correct reason is that the bacteria must amend themselves to the content of the nutrient in the novel medium, has to produce essential amino acids, growth factors, and other enzymes in order to survive.
In the field of microbiology, to inoculate means basically to present or insert one substance into another. For example, one could inoculate a culture of bacteria with some kind of chemical constituent, or it can be said that one introduces the chemical compound into the culture of the bacteria.