There are people who don't own a desktop or laptop at home, or if they do, they use it very rarely. For them, their phone is their primary device, so it makes sense for the screen to be large enough that it's practical and comfortable to use for long periods.
I see others using tablets with a keyboard or the surface pro with a stylus but I don't like the form factor which I have to carry in my hand but not in my pocket. Considering a switch to Samsung Note 9.
I probably use it once a month. The input latency and the small size (compared to a notepad) prevents it from replacing the spiral notebook I carry.
I also understimated how much I'd hate the samsung crap that's installed, and the edge to edge screen is more trouble than it's worth--I'm always accidentally clicking something while holding it.
However iPhones (and some Android handsets too) do support HDMI over their data port. You'd need to buy a cable but they can be got for ~£15 (though you'd be looking more at £40/£50 if you want an official branded one - but I've found 3rd party dongles generally work just as well on iPhones).
The SE was far from a failure.
So I can only conclude that the makers would prefer everyone on larger phones for some reason.
I love my SE though. Battery is so much better than I've been used to.
My own circle of friends and their families must be ridiculously unrepresentative because the SE seems to have an outsize presence, and there's remarkably few huge flagships of any make. There's a couple who still hope every year that Samsung see sense and bring out another S Mini.
If they bring back an SE-sized device it will be a high end one, a X SE for example with the screen size of the iphone 8 in an SE-sized body. I wouldn’t be surprised to see them launch that within 6 months and as a current SE owner I would definitely buy it.
The SE was far from a failure not because of the size, but because for the first time it let people into the iPhone realm at a much lower price (without being just an old phone with a lower price). It had the "new" tag on it, although it was basically a product that Apple could generate by mixing up a couple of production lines with much lower assembly costs. By any measurement, the iPhone SE is an old and technically lacking phone with a superior and hyper-sticky software ecosystem. It was also the workhorse of carriers who could sell expensive plans with a lower device subsidization fee.
Apple's marketing is best in class when it comes to framing the complexity of market tactics and vendor-carrier relationships within a simple and clear narrative. The underlying mechanism are still as intricated as they can be.
Almost no one wanted headphone sockets actually removed because anyone who actually wanted bluetooth already had the capability, and countless surveys reveal a wish to keep them. Most recently Oneplus finding 80%+ of their customers wanted to keep it, so their next phone removed it. Almost every company has now followed suit, so it's damn clear they are not researching the market, unless it's to ascertain the extent of what they can get away with.
Same with Google+, almost no one wanted it, yet for several years there was insistence one would have it.
So I maintain the presence or absence of a product or service is often little or nothing to do with market sales. Or one can believe in perfect markets and perfect filling of opportunities.
On the basis of what?
If I believe it is true that the world is flat then someone may reasonable ask what the basis is for that belief.
Give me an example of a belief with no basis at all.
Spiritual and religious people give reasons and justifications for their beliefs all the time. Have you never heard an argument for why the universe couldn't exist without a god? Surely you're aware of all the arguments made in things like the philosophy of religion?
Even if a belief feels to you to have no basis that doesn't mean there isn't one. People often claim that their intuition about something has no basis, but it's actually that they don't have a consciously-accessible basis -- there's all the actual things they subconsciously picked up about, say, the person who seemed shifty, and all the subconscious mental processing that leads to that feeling.
And they're ultimately all baseless.
EDIT: I also get the feeling that bigger phone means more features and longer battery times because of the extra space for electronics and the battery. Who knows, maybe if I held a 4" that's fast with a lot of memory and long battery life, I could get accustomed to seeing less content.
There's also the fact that website layout is determined by the website developers. I wonder how good the layouts are generally on the internet for 4" screens. It might be that many websites have fixed width side margins that cause a bigger whitespace-to-text ratio on smaller screens.
The 5s has the venerable status of being not only small, but one of the oldest currently-supported smartphones. At over 5 years old, it can still run respectably with iOS 12.
For me the difference is the SE simply fits the hand better. My other half would be even more vocal on that point.
So if the choice becomes 5.5" and larger or nothing, we'll probably be ex-smartphone owners. Speaking for myself I'd go feature phone before I'd "go large" again.