Why can't we take a Guarded Step as part of Trick Attack?
I'll assume "because action economy" isn't the answer you're looking for, so I'm gonna go with : Why would you want to ?
Trick attack already allows a full move, and there are exploits to prevent you from provoking AOOs during that. So same as a guarded step, except better.
It takes some investment (1 to 2 exploits), sure, but seems worth it.
Edit : you'll only be truly free of AOOs at 10, which is later than I remembered, but still.