From the official announcement:

"Frost Giants are a limited race. I know this might curdle your milk, so sit down before reading any further. Are you seated? OK, you were warned. Frost Giants are even more limited than that; with this race I wanted to try implementing something seasonal. So, you can think of the Frost Giant as the McRib of CF. It will likely come and go with the Winter."

[forums.carrionfields.com]