The keighleys are a shitshow in a lot of ways.
My understanding is that it is a VERY small subset of judges who bucket the games into categories and then that is sent to the wider range of outlets.
According to the keighleys themselves: https://thegameawards.com/faq
Nominees for most categories of The Game Awards are chosen by an international jury of over 100 global media and influencer outlets, selected for their history of critical video game evaluation.
Specialized juries also convene for other categories including esports, accessibility and best adaptation.
Each voting outlet completes a confidential, unranked ballot based on the collective and diverse opinion of its entire editorial staff, listing out its top five choices in each category.
Ballots are tabulated, and the five games that appear on the most ballots are put forth as nominees. In the event of a tie, six (or more) nominees will be announced in a category.
Game Awards producer Geoff Keighley is not a member of the jury and does not vote on the nominees or winners. Similarly, The Game Awards Advisory Board has no involvement in the awards process and learns of the results at the same time as the general public.
How much you believe that last bit gets messy and is irrelevant to the topic at hand. But more than a few games media folk have openly complained that the pre-sorting into categories is just complete nonsense and all they can really do is pick what they know of once the final ballots go out.
So that is why you have shit like the Simulation (?) category that is a catch all for sports games, flight sims, strategy games, mobile games, rocket league, minecraft, etc. Similarly, you get cases of "... Dave the Diver is not an indie game but I guess it is the best game in the Indie category?"