Final answer:
The excerpts given do not contain information about Mr. Craven or a secret garden, thus it is impossible to provide an explanation for Mr. Craven's actions without the proper context.
Step-by-step explanation:
The reason Mr. Craven threw away the key to the secret garden is not included within the supplied text excerpts. The excerpts provided appear to be from various sources and possibly different works of literature, and they do not contain information about a character named Mr. Craven or any related context about a secret garden.
As a result, without the correct context or source material, it is impossible to provide an accurate and confident explanation as to why Mr. Craven threw away the key to the secret garden.