Can someone explain dog show winners to me?

So I watched the Westminster dog show last night and they mentioned how the winner had won several shows before. Though I don't question the worthiness of the dog chosen, I don't understand how this happens.

With dozens of breeds, each being compared against their own breed standard, this seems like an impossibly subjective judgment, which shouldn't be easily repeated by another set of judges. Further, there are breeds like the St. Bernard that have never won. What does that say about St. Bernards?

It got me thinking about the internal politics of the event, and whether there are explicit biases against especially niche breeds or whether breeder politics plays an important role here.

Would love to hear some breeders' thoughts on this!