I honestly don't understand why Google got into this business in the first place when there were so many established companies do a much better job than they ever aspired. "Google Affiliate" always seemed like a me-too/just-because-we-can service.
They bought DoubleClick for $3.1 billion... This was their deal.
to be clear DCLK had (IMO, was not in either side of the deal) many valuable assets and technologies. the self-serve stuff that became GAN was a rather small aspect of that.
they bought DCLK for other stuff, this came with it.
DoubleClick Performics was rebranded as GAN. They did not improve the system after buying.