derived allele frequency

A DAF of 95% could be due to:

1. chance, alleles will fix or be weeded out by chance especially if your effective population size is low. Chimps have a greater effective population size but could still fix or weed out variants by chance.

2. positive selection

3. weak background selection

4. error in the inferred allele for the chimp/human. It also implies that there was a single allele back then. It's possible that the one fixed in humans and the other in chimps by pure chance.