Occam's razor? What about any common sense? Note that within minutes from the catastrophe there was already the government camp claiming that this was clearly an accident with no fault on either side and the president camp speculating that this was an assassination. The fact that investigation after that was kind of a bad joke didn't help to silence the second camp.

Because "accident" is how you call such disasters? Also, people in the industry knew the less-than-sterling reputation of governmental transport service.

EDIT: I should clarify that "accident" is a specific class of event in aircraft accident investigation, together with "incident". It's literally "aviation terminology" stuff.

A plane crash caused by pilot error is the definition of an accident. Not intentional, unexpected, and uncontrolled. The scale or tragedy of the accident doesn't remove the fact that it's an accident.

accident:

[1] An unfortunate incident that happens unexpectedly and unintentionally, typically resulting in damage or injury.

[2] A crash involving road or other vehicles, typically one that causes serious damage or injury.

Airplanes don't blow up randomly.

A proof of an explosion (which this is not) would be proof of an assasination.