I assume it has a lot to do with the stall characteristics, but with the SR20/22 having a combined 1.6/100,000 Fatal rate and the DA40 having .35/100,000 Fatal, it seems like a very stark difference. Additionally, the SR-- has a ballistic parachute and the DA40 does not.
Compared to other 180 hp airplanes the DA40 handles strong cross-winds better. It also has good visibility because the canopy bow is so far aft.
In defense of the SR20 what can be said is that the SR20 has a split-airfoil wing design that guarantees the wings will stall near the fuselage first, leaving the outer wings and ailerons unstalled. The result is very controllable performance right up to and including the stall.
That being said, a majority of accidents involving the DA40,SR20/22 or any 4-seat GA airplanes is almost always caused by Pilot error. So , it is not about the DA40 being more safe than the SR20. Splitting high and low fleet hours may result in too high a number. Ergo, the math is not precise.
Not sure how true it is, but one theory I've heard about the high accident rate of the SR22 is the parachute. Every added safety feature tends to make people more careless. Was the same when airbags were first introduced in cars, accident rates shot up for a while before slowly trending down again.
Also, the DA40 is used more often as a trainer, while the SR22 is more often used by relatively inexperienced pilots who do have a license. Might well make a difference (student pilots tend to be more aware of the limits of their skill and knowledge than cocky fresh graduates who think that now that they are certified to know it all they really do know it all). And often that student will have an experienced instructor in the cockpit with him as well.
Suggest you look at the design of the DA-40 vs the Cirrus aircraft. Also compare the number of post-crash fires in each aircraft type (DA-40 has zero). The Diamond's have dual spars in their wings, with fuel tanks between the spars (for crash protection). The Diamond's also have robust fuel lines that resist pinching and breaking in the event of a crash.
If I had to place the blame on this one, it’s in the fact that the Cirrus aircraft are faster and more capable. I suggest reading The Next Hour by Richard Collins about GA accidents and safety. He talks at length about how faster, more aggressive airplanes tend to attract aggressive pilots who may lack the discipline to fly them properly or have extreme hubris in regards to their piloting abilities. Add into this Cirrus’ somewhat deceptive marketing strategies where they seemingly tout the airplane as safe, almost to the point of invulnerable, with the CAPS system. The general public’s and GA pilot pool’s ignorance of the capabilities and limitations of safety features combined with the high performance of the airplane as well as the large scope of private pilot privelages in terms of airplane performance also aggravates this. This make for a situation ripe for accidents to happen.
To be fair the Cirrus SR20 and SR22 are excellent, docile and safe airplanes IF OPERATED PROPERLY. And the SR20 has an excellent safety record, comparable with the DA40. But the fly faster and operate faster in the pattern than does the Diamond. And considering that 50% of GA accidents happen on approach and landing, at low altitudes at higher speeds with more impact energy where the chute is inefficitve as an escape system, it’s no wonder an SR-22 has a higher accident rate associated with it.