Lazy? A little. However, think of it from this perspective. Marks are submitted to them by the WORK department on Friday. So they start using them on Monday. They have to submit a great deal of marks for all subjects during this time period (WORK isn't the only department to submit marks). They would then have to enter them onto the database for each student. Then I'm sure someone has to double-enter them to make sure there are no errors. However, I'm sure errors occur (e.g. you may have a mark of 22 as WORK screwed up the entry of your essay), so they would have to contact WORK and double-check that there was no error made, and you did in fact receive a low mark.
Eventually after all errors are sorted, they would need to put all the results online.
Ideally this process should take 2-3 days, but often it does take longer.