Here's why:
* Prepositions show the relationship between a noun or pronoun and another word in the sentence.
* "According" is often followed by a noun phrase that indicates the source of information or the basis of an action.
Example:
* According to the weather forecast, it will rain tomorrow.
In this sentence, "according to" shows the relationship between "it will rain tomorrow" and "the weather forecast." It tells us that the information about the rain comes from the weather forecast.