The chromosome in bacteria is circular in shape while that of humans is linear. The replication of DNA in humans does not happen to the complete end of the chromosomes unlike in bacteria. Hence human DNA shorte with every replication.
Human DNA has introns (non-coding regions) while bacteria DNA does not hence replication of chromosomes is complex in humans. In addition humans, DNA is supercoiled with histones that have to be uncoiled for replication to occur. Bateria chromosomes do not have histones and uncoiling is not as complex.