There are technical reasons. The rules are very clear in the event of a tragedy: the first country under suspicion is the one where the incident occurred. The second is the country represented by the airline, and the third is the one or ones where the aircraft was built.
The main countries under suspicion in this case are Iran, Ukraine, the United States and France. France builds this type of engine.
As we were on site as expert observers, we were able to determine from the black boxes what had happened in the aircraft but unable to obtain complete answers.
However, the most important thing is to find out what happened on the ground. Why were missiles fired on that aircraft? Who gave the orders? Why wasn't the airspace open? The answers to those questions won't come from the black boxes, and they're the ones we're looking for right now.