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This is likely due to the combination of popularity and the 4th series numbering of Mr. Robinson's rookie card.

The 4th series is notoriously tougher than any other in 1957 (typically it is the last series in other issues but not here)

Brooks has legendary status among his fans, definitely a bigger collectible fan base than the other rookies in 1957. Among Baltimore Orioles fans, he's probably their biggest star.

I am not sure about Musial in comparison, but the 1948 card is not his first actual playing year so that may play into consideration on pricing. His high grade versions are still expensive...and his star power is quite high.

Kiner cards are not a good comparison. Despite his HR hitting prowess, he is generally not considered an all-time great among his contemporaries, but Brooks certainly is in that argument.