That’s not completely true, see the first draft of Marker Proposal where they pointed (see date also):
As the incentives to scale Ethereum are aligned between MakerDAO and Optimism, it’ll be a great deal for both communities to save a % (up to Optimism’s governance) so that the Maker governance gains voting power in the governance decisions.
And this topic was duly discussed (authors removed it after an initial feedback but perfectly if it had been maintained and approved by others there would be no problem).