If you look back waaaaaaay in Part 1, Spike does speak the trigger to Alex and it doesn't work (it's specifically stated by Spike that the question "Do you want to see the alligators dance with the elephants?" is the trigger.)
It's been heavily hinted all along that the books Alex would get (again, Part 1) from Ms. Smythe contained the ever-changing trigger phrase, but that Ms. Smythe had forgotten to give Alex a book and that's why the trigger didn't work (because he never got it).
And in Part 5, Spike asks for a new trigger and Giles refused to give it to Spike. The story above you in Part 6 explains why Xander has to remain Alex — psychic monsters are looking for Xander's psychic signature. The only way the monsters actually know Alex is Xander is if: 1) Xander breaks through somehow; 2) they physically see him. Other than that, Xander can't be found.
As for why not a more capable one, that'll be answered in Part 8, as will Spike's constantly making Alex drink water. *whistles innocently*
no subject
It's been heavily hinted all along that the books Alex would get (again, Part 1) from Ms. Smythe contained the ever-changing trigger phrase, but that Ms. Smythe had forgotten to give Alex a book and that's why the trigger didn't work (because he never got it).
And in Part 5, Spike asks for a new trigger and Giles refused to give it to Spike. The story above you in Part 6 explains why Xander has to remain Alex — psychic monsters are looking for Xander's psychic signature. The only way the monsters actually know Alex is Xander is if: 1) Xander breaks through somehow; 2) they physically see him. Other than that, Xander can't be found.
As for why not a more capable one, that'll be answered in Part 8, as will Spike's constantly making Alex drink water. *whistles innocently*