Why does Dexter find spring dismal and the fall gorgeous and full of hope?

In "Winter Dreams," Dexter loves the fall because it allows his imagination fuel powerful dreams that cannot be envisioned in the spring.

Dexter finds the fall's "full of hope" animating his dreams.  In the fall, Dexter's dreams define his existence.  He trembles with anticipation and excitement at these aspirations.  Dexter is able to "make brisk abrupt gestures of command to imaginary audiences and armies."  He is able to envision how he is the golf champion at the club, and how he is able to attract admirers.  The fall is where his dreams come alive.  

However, in the spring, Dexter's reality emerges as a caddy.  His daily life as a caddy who does his job well fades in comparison to the life of dreams that he sees in the winter.  In his work as a caddy, he is not able to command the attention of everyone in the club, and he lacks the elements that serve as "ready grist to his mill."   The gulf between reality and dreams is the reason why Dexter finds the spring so vastly different than the fall.  Dexter's "Winter Dreams" can only be seen at a time when reality does not interfere with them, and represents why he sees the fall's hope as superior to the dismal reality of the spring.