I just assumed that USA three letter agencies paid larger companies upfront to implement back doors; seems to fit with past form. Why would they not do that. Indeed it always struck me the debacle with Huawei where USA government smeared then to prevent their equipment being used in UK was so that USA-manufactured equipment with USA-controlled backdoors would be implemented instead ... it might only have been financial protectionism but it just seemed too big a protest.
/tinfoilwrappedforfreshness