That's technically correct but what you fail to take into account is that there are Samsung users who don't won't to look elsewhere and want to specifically buy Samsung phones-just like a typical Apple user.
I'm personally one of them. I still have a Galaxy S5 and am looking to replace it with another Samsung. This is the reason people get so frustrated as for some, Samsung is their only real option. I personally just like all the features over and above other Android phones and prefer having a phone that has the best features like the camera plus extra like iris scanning, Bixby etc.
Also, when my Galaxy S5 is still running perfectly after almost 3 years it encourages me to buy Samsung again. Though I won't get Nougat, I am still getting regular security patch updates which encourages me again. If I buy a Oneplus for e.g., which I'm sure is a good phone at a cheaper price, will I still get security patch updates in 3 yrs time?
Basically, I trust the biggest Android OEM for a combination of features, performance and longevity. The price doesn't concern me.