I don't see any evidence of this being part of their random name-slapping or them simply not trying hard enough.

Hasbro may have been unable to trademark Straxus and Octane, and/or were unwilling to expend the time, effort and money to attempt to fight in court against whomever happened to have the very similar trademark, especially as, in these cases, Hasbro doesn't look like it had much of a legal leg to stand upon.