Value of the 1+1 bundle
Many reviewers explicitly cite the buy-one-get-one 300mL set as a major reason for purchase, calling it a bargain that lets them stock up and use the product liberally.
Brand trust / line extension from Dokdo Toner
A large number of buyers were already loyal Round Lab Dokdo Toner users who purchased the Birch Juice version to try another product in the trusted line, especially for drier seasons.
Reputation for gentleness on sensitive/reactive skin
Reviewers with sensitive, eczema-prone, or reactive skin sought this out based on its reputation for being non-irritating and fragrance-free.
Word-of-mouth / hype and recommendations
Several reviewers mention buying it because it is 'popular in Korea,' recommended by Korean users online, or because of general hype around the brand.
Repurchase after running out
A very high proportion of reviews are 2nd, 3rd, or 5th+ repurchases, indicating strong loyalty once tried.