... but the parachute? Really? If you know the speed and the density of the atmosphere you're going to deploy it in then the rest is basic physics and engineering. Just make sure you make the damn thing strong enough!
You would think so, yes, except that no one has developed a parachute precisely (or even remotely) like this one before: it's the biggest super-sonic parachute ever (the ring portion of the 'chute deploys at over Mach 4 ... normal aerodynamics don't work there), AND, it has to be light enough to meet mission parameters for weight budget. While you might think it's basic physics, the empirical details are a bear to get right.
It's not just that this is, in fact, rocket science, but really, really hard, cutting-edge rocket science.
Having watched the NASA-released video, the failure mode appeared to be very different from the first test. The first test suffered from imperfect deployment that resulted in uneven loading and thus failure of the main 'chute. The droge (the first little 'chute) went out perfectly, but the main parasol failed to open. The second test failed more quickly, without even partial deployment of the main 'chute, as if it was immediately ripped apart. Watch the videos, they're fascinating!