People that are self employed tend to need to do self-file, or those with slightly more complicated investment approaches but even then that's generally not a particular hard task.
One of the other advantages of it, is it discourages a rebate based approach to incentives. With most people not needing to file taxes each year, rebates wouldn't be particularly effective at encouraging behaviour. The government instead opts for subsidies, so the item is cheaper _at the time of purchase_. No shelling out the extra money and then eventually clawing it back, without any interest it might have accrued for you.
It was quite a shock when I moved to the US and got to experience the "delights" of filing taxes here.