Pretty sure it's just because if the tool generates the commit, it auto-adds itself as co-author. Like the iPhone emails that say "sent from iPhone"
Yes, but the equivalent of "sent from Invasive·marketing·of·some·MUA™" would be "generated with Ludicrious·Laughable·Mockery™".
That is, the MUAs don’t add "co-authored by myMUA".
Waiting for the day I get an email from someone that says "co-authored by my iphone"