I assume it's because the Machination Sunstreakers are like Transtectors - sparkless bodies. No idea what happened to Sunstreaker's real body, as it would contain his spark casing.
I assumed that Hunter merged with Sunstreaker's actual body when he escaped the Machination, but need to reread to be sure.
Meanwhile i_amtrunks I like the term "Streakers" for the clones. About time there was an Autobot equivalent term for "Seekers"