I'm sure the copyrights on names and characters coming up due had absolutely nothing to do with it.
What?
There are no "copyrights" on names (you're thinking of trademarks), and copyrights on characters surely don't expire that quickly (and once they do, they're gone, finished).
Also, trademarks being under threat of expiring every few years if they don't get used in commerce is an ongoing concern for Hasbro that wasn't limited to one specific point in time. It's just that their priorities which trademarks they feel are most worthy of keeping shift over time.
Meanwhile...
No, but he was back when the mold was in use, and he and his team were always looking to the future, how to make things new and different from what all came before, rarely ever making homages to G1 at the time.
The real G1 homages didn't really start until Energon, by which point the mold was long since out of use.
This was the guy that always kept saying "No" to every fan request at BotCon for a return of more 1980s G1 characters and concepts.
It took the switch from Archer to Warden for us to really get that return, which we've had since Combiner Wars onward.
That is also incorrect. First of all, while Aaron got promoted from lead designer of the Transformers brand to "design director", he was still very much in control of the direction of the brand throughout Energon and Cybertron (which was also when the Alternators line happened).
Also, Warden supposedly didn't get involved with the Transformers brand until sometime around Thrilling 30. Before that, we had Classics, we had Universe, we had 2010 Generations, we had Reveal the Shield, and we had a shitton of G1 homages in the movie lines. Claiming that Warden is the main reason we ever got G1 homages is a gross rewriting of history.