[General] I thought it was amazing...

[NAL123]

I've heard the judges of many talent shows say the following sentence after a contestant performs in front of them.

Show host: Judge A, how was the performance?

Judge A: I thought it was amazing....

Why don't they say I think it was...?

 

[GoesStation]

I think: I currently believe.
I thought: I believed during the performance. This doesn't exclude believing the same thing now.

The past emphasizes how the performance affected the person while it was going on.