There isn't any one cause. Each disaster has it's own causes. Most likely you're just identifying what you perceive to be a pattern (grouping of air disasters) in recent memory. It's kinda how people say "deaths always happen in threes" when two celebrities die in close proximity, and then people wonder who the third is going to be. Logically, that makes no sense, it's just how our brains are wired to see patterns and is a type of information and confirmation bias.