It works for me because:
It’s quick and simple. I just keep the planner open on my desk and it takes a second to write down the task. As easy as many time tracking apps are, they require too many steps to add a block of time in the past or future.
It’s tactile. As silly as it sounds, there’s a small but subtle pleasure reward in using the highlighter or even adding a sticker to the page. (I’m stingy with stickers, though.)
It’s colorful. Again, it’s the small things. On the days when I’ve forgotten or been too busy to keep up the log, those blank white columns are a sad reprimand. It’s like nothing happened at all those days, even though I know something must have, so I’m motivated to keep tracking.
It’s actually enjoyable, something I’d never thought I’d say about keeping tabs on every half hour of every day.