Thanks for your posts on this.
I’ve found some further information relating to this feature.
Amazon’s Choice is a feature that helps Amazon customers save time and effort when searching for common, everyday items and suggests highly-rated, well-priced products with Prime shipping. Amazon’s Choice is not available for all products.
Sellers don’t need to enroll or register to be considered for Amazon’s Choice – the Amazon’s Choice feature considers all highly-rated, Prime-eligible items sold or fulfilled by Amazon. It’s not possible to specifically request that your product be selected as Amazon’s Choice for a given search keyword.
Selections are constantly updated, so continuing to offer high quality, well-priced products to your customers will give you the best chance to be selected as Amazon’s Choice.
I hope this helps.