In other words, they contain more regions of DNA that are expressed. The idea that genome density decreases as the complexity of the organism increases hold true. This is due to the fact that eukaryotes have a much stronger presence of introns than prokaryotes.
Essentially, these organisms contain more segments of DNA that are expressed. It is accurate that genome density decreases as an organism's complexity grows. This is because eukaryotes have a much stronger presence of introns than prokaryotes.