Early on Hasbro's response was there "too many tank like vehicles at that size" at the time, which made fans blame everything from Dropshot to Onslaught, but it was a Takara Designer in a translated interview that revealed the reason Galvatron got shrunk from Voyager was because there was Animated Shockwave was already a multi-mode gray tank robot.I keep coming back to Galvatron because it was such a head scratcher that encompassed all the insane doublethink of that era.
It's 2008, movie stuff is big, and kids don't know what stuffy G1 is. So to make G1 stuff in Universe viable it needs to look and feel like the movie stuff. So alt modes and colours need to be realistic! Galvatron can't be a weird purple space cannon, he needs to be a realistic grey tank!
But also his giant translucent orange cannon barrel can be the grey tank's barrel because...realism...
That toy had so much wrong with it, and I grant the at the time team a mulligan in that some bean counter forced them to downsize it, but even accounting for that the ethos was all wrong.
Translated interview here.