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.

Quote Originally Posted by GoktimusPrime View Post
The merging of the two consciousness between Dante and Scorponok appears to have occured far more rapidly than it did in G1 between Zarak and Scorpie. It'll be interesting to see if this merger occurs with Hunter and Sunstreaker as we've never seen a true mind-meld like that between an Autobot and his binary bonded parter since Optimus Prime and Hi-Q... and even then, let's face it, it was pretty much Optimus Prime's personality that took over. Hi-Q's consciousness was effectively smothered when he was merged with Prime. Fortress Maximus and Spike had a symbiotic mental bond, but both consciousnesses remained independent of each other (moreso for Spike though). Hunter and Sunstreaker could become the first proper mind merge between an Autobot and his bonded partner! Hrmmm...
I SERIOUSLY, SERIOUSLY doubt they'll have Sunstreaker and Hunter truly merge now. Hail and Farewell was Simon Furman's glimpse into his future storylines (at the time he didn't know All Hail Megatron had already canceled his plans), and we saw Hunter and Sunstreaker merged together, in that Hunter's family are now Sunstreaker's family.

Considering the stuff Furman had to drop, I think we'll see the Hunter plotline over-FINISHED by the end of Maximum Dinobots so Sunstreaker can go hang out with Sideswipe in AHM

IDW doesn't like complex storylines anymore.