United allows Phuket but not Tokyo

I'm planning an award trip on United for summer 2014. My dates are flexible.
San Francisco to Paris to Phuket to San Francisco.
SFO - CDG - HKT - SFO, it charges 65,000 mile economy per person. A lot of flying on economy, I know.

My wife wonders about Tokyo instead of Phuket.

SFO - CDG - NRT - SFO, through online it doesn't take. I plan to call.

1. Any reason why HKT worked and not NRT online?
2. If I include NRT instead of HKT is it more miles?

Thanks.