It's the exact same as reaching level 50 online. People want level 50 in CT to use it to expliot the game. Only real difference is that you can't prestige on CT until treyarch release a patch.
That is not true you can prestiege on combat training.
1. Let your mate invite you.
2. Hover over Playercard > Prestiege
3. Tell friend to switch lobby to combat traiining
4. You can now buy emblems and titles and prestiege
5. Just a little thing if you get to say 3rd on cb training then you can buy that prestiege title and have it online.