Is that it's been happy enough to rest on it's laurels since the S3.
After losing my iPhone 4 at a festival I was swayed by the S2 and picked one up - I was impressed with the specs of the phone and how it was better than the iPhone in every way, I was impressed enough to upgrade to the S3 with it;s larger screen, extra memory and SD card expansion.
Then the S4 happened and I didn't feel that the improvements warranted a purchase and then the S5 caused a similar lack of impressedness with a lack of innovation with the design and the extras (airtouch? Fitness? even as an avid gym goer these didn;t float my boat).
What I ended up looking for was a phone that had the externals that I wanted, at a price I was happy with so the things that matter to me:
SD Card slot
Front facing speaker (as I use my phone as a radio when cooking)
I think that Samsung's issue is slavishly sticking to a form which it can produce but showing no changes in ideology for how the sound is produced by the device (possibly the lawsuits didn't help either), and lack of updates for Android OS for the phone.
Oh yeah, and producing duplicate apps of all the cones supplied by Google too...