Why is the proportion of sequences anchored to chromosomes low?

[XXH123a]

Dear Chenxi，
Compared with 3d-dna, yahs' scaffolding speed and clustering sorting accuracy are so excellent! My genome is about 1g, and the heterozygosity is less than 0.2%. I am curious why only 91% of the sequences are anchored to the chromosome, while 3ddna is easily as high as 97%. I don't know whether this is related to species. If we don't consider the influence of sequencing depth of Hi-C data, can we think that the main reason why there are no anchored sequences is that the alignment quality of these sequences is lower than Q10, or that these sequences are redundant parts generated by the assembly software?