He thought it was a giant with long arms
It benefited in numerous ways but mainly it and maybe most importantly it gave them the access to the China trade. The Pacific route was also Spain's exclusively for a certain period of time and there was also a great need for silver in China which was supplied by the Spaniards from their silver mines.
The answer could be that how his family and White House mislead the public about his illness. James Reston comments that journalists do not take the health of candidates seriously and that needs to change.