Projects get completed right before their deadline (if you're lucky). Design complexity increases with time (even for simple bugs). Software developers write programs to use as much CPU and memory as possible (try running Google Chrome and Slack).
I'd write fluff in school to reach an arbitrary 500-word requirement. Now, I get to the point.
Work expands to fill the space.
Constraints sometimes inspire creativity. Often, I'm most productive in the short blocks of time between tasks on my busiest days.