I think it is because if you make a mistake, you will pay for that mistake in combat. I remember my first few playthroughs of Demons getting killed by the beginner Slave dudes just because I rolled into an attack too early and got hit with their wild swinging attack lol. Bam Bam Bam Bam dead ... Fuck. Or the blue knights, if you messed up and attacked too soon they would counter and stab you in the gut, taking out half your energy or more, killing you if you were lower on health.
Various things like that. In Demon's case though, it really stacked the deck against you. It actually punished you for dying too much lol. Not only are you only half health when dead, if you drop into the black world tendency the games enemies get even harder. They had more health, hit harder, etc.
The Souls games are hard, lets not boast too much here lol. I'm sure even you, with all your careful consideration of every battle, ended up dead more then a few times.
It is fair though, def. You learn from your deaths because each one has a direct cause, likely akin back to something you did wrong.
I died plenty of times, very rarely due to the game's fault. I think one of the few times I died due to the game's fault was when trying to navigate, for example, the wood planks in Demon's Souls 1-1 when you were trying to get the items on the way down to the highest-defense armor in the game.
When I died in Demon's Souls it was because I was inexperienced, reckless, impatient, nervous but I never felt once in any Souls game, when I died that it was hard. I always felt that it was challenging, I always felt that the challenge that defeated me was trying to tell me something, and I wasn't responding to it correctly.
I tried passing Demon's Souls by grinding levels in Shrine of Storms and quickly discovered that levels weren't impeding me, as they had only made the challenge slightly easier and I did struggle with understanding what was stopping me from progressing. But once I did, once I discovered how parrying worked, how my guard worked and how it could sometimes be broken, how to avoid certain attacks, how certain weapons were more effective than others in certain situations, it all suddenly clicked, and what seemed to be, at first glance, challenging scenarios became simple tests of the mechanics I had learned and I managed to pass the game by accomplishing and passing some of it's toughest challenges.
Rather than simply feeling satisfied for the experience I had just had when I finished, I felt like I had become a better player. Like I had honed myself into a better person through skill, observation and execution, a feeling which I hadn't held in many years.
So again, I disagree with you. Souls games are not hard. Perhaps I should phrase it like this: Souls games are as hard as the least observant you want to be.