I believe there was possibly the combination of:
1) Mitt Romney’s campaign. And especially...
2) Her young daughters
Which caused Palin to hold off this time.
Next time, I do not believe she will hold off.
That is just me thinking that, but I think she’s in.
Her timing is often prescient. It’s as if she keeps in touch with Someone Who can see into the future.
I trust her decisions whether I like them or not.