Confusion about some things in the later issues of the Marvel G1 comic.

OK, there's a few things that confuse the hell out of me in the G1 Comic. First off, Starscream and Shockwave, along with passengers take off to Earth to attack a "Transformerless planet." However, after the ark blew up, and Galvatron attacked Earth, Fortress Maximus and Spike were still there. Now hang on. Shouldn't Max and Spike have been transported to Cybertron with the rest of the Transformers to fight Unicron? Or was this explained earlier in an issue I haven't read?
Also, why does Megatron stick around on the Ark and walk right into Galvatron? Being Megatron, shouldn't he have blown a hole in the side of the ark and taken off back to Cybertron to retake command of the Deceps?
Also, why does Megatron stick around on the Ark and walk right into Galvatron? Being Megatron, shouldn't he have blown a hole in the side of the ark and taken off back to Cybertron to retake command of the Deceps?