I've been gaming long enough to remember my dad's Sears Pong, had "screen time" limits on my Atari 2600, and still have to have the latest consoles the day they come out. There is no genre that is new or unfamiliar, and while I can beat challenging "1-difficulty" games, like Bloodborne, if given the option, I will always take the easiest way to the end, and most of my peers I've spoken to whom have also been gaming for decades feel the same way. 
The most common consensus is that time is too limited as life's responsibilities increase.  When I was young I had endless time to game, even in my 20's I could sit for hours every night in awe of the innovation that came with the Saturn/PS1 era games. As career duties increase, relationships form, and new generations of gamers are born, time for anything becomes more challenging, and if you offer me a quicker route to the end I'm going to take it, as long as I'm still able to see the same levels and get the same items.  Many dads don't get uninterrupted game time until the kids go to bed, and I rarely get more than a couple hours before I'm asleep on the couch with the controller in my hand.  I spent over 100 hours on Persona 5, and wish I could get 60 back - a younger me might have seen the playtime as a value, but an older me sees that as an imposition. I like to play as many games as possible, and easier difficulties, in most cases does not make the game boring, it actually becomes more enjoyable. 
The other common reason, that will certainly become more significant with time, is that your reflexes diminish with age. The original gamers who grew up going to arcades in the 80's have not stopped gaming, but are now also starting to get mail from the AARP.  An E-Sports study showed a parallel with traditional sports, demonstrating how your gaming reflexes diminish significantly after age 30, and as someone approaching 50, I'm not embarrassed to say I just don't have the "twitch" like abilities I once had, which removes all the fun (the most important part!) from many games on harder difficulties. It won't be too long before senior homes start advertising their network speeds and LAN capabilities. 
I'm sure, if it's not already being done, difficulty can eventually be scaled to the player's nuanced abilities similar to level scaling in many games today. For now, I appreciate the ability to choose, but as a veteran player who skips most cutscenes, most developers are totally missing the mark on who and why people play on "easy" difficulty.