Many documents have content which includes formatting. Many documents are already being created as part of a substantial process, resulting in paper - database reports are an excellent example. Since they are already being printed, they are already in PCL and there is essentially no additional effort needed. Using PDF or HTML requires conversion steps that can be expensive, inaccurate and difficult to efficiently implement. All other formats require some sort of conversion process which can and does modify the original appearance.
Many documents have thousands of pages of related information.
Breaking them apart is an artificial process that makes their management much more difficult. Sophisticated PCL products are becoming available which allow viewing and using individual pages or ranges of pages from large original PCL files, such as huge reports or print jobs. All other formats are the result of often inaccurate conversion processes. This gives PCL strong and unique advantages in many application domains.