I like having the squared off edges for multiple reasons.
One being that the edges lightly dig into my hand, providing grip and more confidence that the phone wouldn't slip out of my hand.
Another reason being that I am able to stand it up on its side if I need to.
More on the gripping the phone, I went from the original iPhone, to an 4s (which was my favorite), then 5s, then 6s Plus when they launched. The 6s Plus would sometimes "pop" out of my hands due to the rounded edges and smooth aluminum. I didn't like the size at all unless I could have two hands on the phone, which I found out was very rarely, as I was almost always using it one-handed.
After my wife broke the screen of the iPhone 5s I gave her (which was given to her because she broke the screen of her iPhone 5), I got her an iPhone SE1, and a Otterbox Defender case.
When putting the SE1 into my wife's new case, I was holding the phone, and just loving the way it felt in my hand. Love the squared edges and size. I wanted an SE, but didn't want to drop from 128GB on my 6s Plus to only the max of 64GB that was available at the time with the SE1.
I ended up switching to the SE1 when Apple released it with 128GB storage.
I sold my iPhone 6s Plus for really cheap to a good friend that wanted an iPhone but didn't want to spend that much for a phone. The ironic part is that he hated the squared edges of the prior iPhones, but loved the rounded edges of the 6s.
So, people like what they like.