Rh factor and dominance of gene
There are various factors which decide the dominance of one gene over the other. Owing to the complex biochemical pathways it is difficult to predict which gene is dominant unless we know exactly how the gene is translated to protein and how the protein interacts with the body.
These are the few answers that could help:-


What makes a gene dominant or recessive
What determines if an allele is dominant or recessive?


As for your question;

There are two genes:


D- The allele which is dominant
d-The allele which is recessive.


A recessive gene is a gene that is nonfunctional or expresses its characteristic phenotype in presence of an identical allele.

For a person to have Rh negative blood group he must inherit 'd' allele from both the parents as it is a recessive trait.And as @swbarnes2 mentioned in the comments 'd' allele is more common in European countries leading to a wide range of population possessing Rh negative blood groups.