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The national/international boys probably don't know our part of the world exists so any SEO is just part of their
overall site optimisation.
Then add in the Adwords 3 pack at the top, the bias to "authority" sites such as Expedia, the multiple Trip Advisor pages that take the visible organic listings
...getting good backlinks doesn't happen because none of the competitors at the top will link to you.
And links from elsewhere just don't have the oomph to make any impact against those already at the top.
I doubt if it is as much brand bias to authority as it is making good on giving preference to Internet Association lobbying partners. Both TripAdvisor and Expedia are proud participants
Yes, and they're equally proud participants in Fairsearch.org, a lobbying organization that exists solely to lobby against Google.
...why SERPs may tend to favor big brands...
So what is it that unfailing elevates this boiler plate churn above the competition?
Google doesn't ever want to make changes that would impact more than 1-2% of results, some people use Google to find a site repeatedly and they know exactly which site they expect to find for their given search.