I go largely by the G1 cartoon, which basically places it as the Decepticons are war machines programmed for war, and thus are hardwired for battle and conquest. It's not their fault, they're just programmed like that. The Autobots just don't dig being slaves, so they rebuilt themselves into semi-capable fighters, albeit notably less powerful (as a general rule) than their Decepticon foes. Hence also why the G1 Autobots tend to be more 'cowboy' than 'soldier' - they don't have the inbuilt discipline/obedience of the war machine Decepticons.
It's kinda determinist, sure, but it makes sense.

The Odieverse has a much more detailed plotline involving Primus using the Quintessons as unwitting pawns to create the TFs as a unified race to destroy Unicron, but that's just my own little microcontinuity.