Because people rarely go to space, and it was much more dangerous when the last person died than it is today. The vast majority of flights are unmanned, just like this test was.

If you want to continue playing apples to oranges though, nobody has died on a spaceflight in the last twenty years. How many have died on airplanes in that timeframe?

[correction: there was one additional fatal flight in 2014 with the destruction of SpaceShipTwo. I would argue that one doesn't count, though, as it was more akin to a relatively mundane aircraft accident than anything else.]