I am wondering the same thing. Please keep in mind that three fellow pilots died in this accident. Tragic to be sure. I would hope that as the details and facts of this accident come out, that we can all learn from this accident. In the meantime, please say a prayer for the loved ones left behind.
I don't know what happened in this situation but just from judging by where this happened I think I can safely say that the same lesson will come from this accident as many more that have happened in this same area and probably any other "practice area" that is listed on a chart or is commonly used as a practice area. The problem is that people ignore the lesson.
When you are flying out of an airport that is near a city, you can't just expect to leave the pattern and start running through all the flight maneuvers in .5 and be back at the airport to get in a couple landings before you crack the $200 mark on your training flight. Students need to realize this and instructors need to stop giving in to it. Go fly somewhere farther away from the busy areas right around airports.
Just because the chart lists a frequency, and the FAA advises that you do clearing turns before each maneuver doesn't mean you will be safe. Those guys involved could have done everything perfectly by the book and that high wing and low wing combination can negate it all. As a pilot, you are trained to make smart decisions and to me, going into an area that you know there are multiple other aircraft passing through and doing maneuvers is not the best idea.
From Long Beach it only takes about 10-15 minutes or so to get back behind the Santa Ana Mountains, even less to go down to the Dana Point area and this little trip gives you an actual real life flight to negotiate. It will cost a little more than doing those stalls as soon as you cross that dotted blue line on the chart, but you are buying safety. If you can't afford that, then maybe you should pass on buying some other safety features too. Who needs those seat belts? Fire extinguisher, those are expensive, current and proficient, can't afford it.
So back to the original point... What we need to learn from mid-airs that happen in known busy areas is, it's a big sky, using more of it will decrease the amount of accidents like this.