Question on Frostfire Talent Build in 12.0

[Flexcalibur 0]

Hello! So I was going over the guide for Frost mages, specifically the Frostfire Single-Target build, which currently is not recommending we take Thermal Void and if I am understanding the guide correctly, not using Ice Lance at all. However, the recommended talent build picks up Flash Freeze in the 6th row, which gives Glacial Spike a 100% chance to grant Fingers of Frost. Is there an interaction I'm missing as to why we would take this talent? I could see it just being a filler, except we could definitely take Freezing Rain instead for the times we did have to do any AOE. Just wondering if I am missing something.

Thank you!