If it was irrelevant then why did the FBI make such a big deal about it? Are you saying the FBI did that just to make Apple look good? Why would they care about Apple's reputation?

Well in theory more people use an insecure software, the more FBI can monitor

Yes. Apple is one of the largest companies in the US, and the NSA did them dirty by letting it become public that Apple is cooperating in allowing them to conduct warrantless surveillance. The alternative is Samsung, and the US government would prefer people buy iPhones. We’re also not just talking about the USA, but the 240 million iphones sold each year.