BV,
I guess because he sold himself well. And papers, including the Telegraph, may not realise that his bio shows his somewhat sheltered 11 year RN career as being focussed on ship ops, diving, mine clearance and IED disposal. Nothing much relating to the other two services, on which he writes as it he were an expert, and nothing that would have given him any experience of defence procurement, on which he writes as if he were an expert.
As for his credentials to comment on aircraft, air ops or the RAF, well, he did spend some time at a UAS. Can't find any Army connections there.
The Phoenix Rant Tank are bound to snap him up!