Why are there so many songs about rainbows

...and so few about books and/or rock stars?
Well, here's a few:

1) Be My Yoko Ono (Barenaked Ladies)*
"If I was John, and you were Yoko, I would gladly give up musical genius/just to have you as my very own personal venus"

2) The Book I'm Not Reading (Patti Larkin)**
"The book I'm not reading is better than TV"

3) Brian Wilson (Barenaked Ladies)*
"Just listening and relistening to Smiley Smile/And I'm wondering if this is some kind of creative drought"

4) Everyday I Write the Book (Elvis Costello)**
"you said you'd stand by me in the middle of chapter 3/
but you were up to your old tricks in chapters 4, 5 and 6"

5) Gimme Mick (Candy Slice aka Gilda Radner)*

6) I Could Write a Book (Rodgers & Hart)**
"I could write the preface on how we met/So the world would never forget"

7) Lou Reed (Little Willies)*
"And we hope our perceptions isn't slippin/But we swear to God we saw Lou Reed cow tippin"

8) My Baby Loves a Bunch of Authors (Moxy Fruvous)**
"I like to go out dancing/My baby loves a bunch of authors/Lately we've had some friction/ 'Cause my baby's hooked on short works of fiction"

9) New Biography (Van Morrison)***
"How come they've got such good memories/And I can't even remember last week?"

10) Talking New Bob Dylan (Loudon Wainwright III)*
"The real world is crazy/You were deranged/An' when you went electric, why, everything changed--"

11) When I Write the Book (Nick Lowe)**
"When I write the book about my love/It'll be a heartbreaking story about love and luck"

12) Wuthering Heights (Kate Bush)**

*= about rock star(s) **= about book(s) *** = about both