Well their sales suffered as "not-iphone" too. Really it's hard to find an explanation for what's happening.
For the past few years, they have increased their flagship phone price to match the iphone. The dropping of Flash support (though not Samsung fault) doesn't help along the way.
This is where the Samsung phone users started to split between budget phone users and flagship expensive phone users. The budget phone users switched to other android manufacturers, while the flagship expensive phone audience switched to iphone or hold onto the S5.
Samsung and its fanbase shone and exaggerated the 'flaws' of iphone, and now its slapping them back in the face.
Samsung trolled competitors with its S5 waterproof ALS ice bucket challenge video.S6 has got no waterproof now
Samsung trolled iphone with the wall hugger ad, touting its removable battery. S6 has got no removable battery now.
Samsung attacked iphone's bendgate. S6 faces a bendgate of its own that's as severe if not worse compared to iphone's bendgate.
Samsung should be glad nobody picks up the
scratched screen controversy yet.