The condensed form of DNA that exists during cell division is tightly wound and therefore unavailable to the enzymes and transcription factors that interact with and read DNA. So, if chromosomes are constitutively condensed, the cell will not be able to transcribe RNA, and thus will not be able to make new proteins, and thus will not be able to grow and divide. The process of selectively condensing certain regions of DNA to prevent binding of transcription factors and RNA polymerase is actually a conserved method of epigenetic transcriptional regulation in eukaryotes.
You may be thinking _Then why condense DNA at all?_
Uncondensed chromosomes are difficult to separate, and failure to properly segregate homologous chromosomes during mitosis (a phenomenon called nondisjunction) can lead to aneuploidy. Aneuploidy in germ cells is often lethal, and aneuploidy in somatic cells is a characteristic of cancer.