I suspect it's because the original Note 1-4 phones were too good. Almost everyone I know who had one kept their phone for at least 4 years before even considering upgrading. This was great for consumers, but bad for business.

Now, the Note line is closer to the Galaxy S series. This makes them more fashionable, which attracts a lot more buyers, but it also removes the features that made the Note line so long-lived like replaceable batteries and noticeably better hardware

I really wish someone made a flagship Note competitor. Ever since the Note 4 (the best Note), it's been going downhill. Now I am not saying that Note 5 and above are bad, they are decent phones. Just ever since then the Note has been going away from its roots and becoming more and more like the S. (which again isn't bad, but simply not what those who started with the note were looking for)

Note was suppose to be the utility phone. The S Plus was suppose to cover for those Note users who were there only for the large screen. But instead we lost more and more utility with the Note. Note usually had a processor upgrade, but no more. Larger battery, but no more. Removable battery. The S Plus corners look sleek and nice but not ideal for note writing.

With Note being so successful, I'm shocked no one tried to copy it.