One UI to rule them all
One UI to bind them
One UI to grind them all
And in it's brightness, blind them.
I don't know what has gotten into the collective consciousness of people directing "modern UI design", but in my opinion they pretty much all need to pull their head out of the clouds and actually think about the effects of their design choices on their customers.
Windows 10, and Android Lollipop are two classic examples of problematic UI designs. They feature lots of stark, bright white all over the screen - windows, notifications, settings pages, etc. As someone who is both prone to migraines, and has an autoimmune disease that makes my eyes light sensitive, those bright-white screens cause me continual, severe, physical pain. I'm not alone either...there's a significant segment of their users that experience these issues. Just look at google, and you'll find numerous complaints matching mine. In both Android and Windows, I as a user have been locked out of changing the system UI theme to one that doesn't cause pain.
Torture: (from Merriam-Webster)
: the act of causing severe physical pain as a form of punishment or as a way to force someone to do or say something
: something that causes mental or physical suffering : a very painful or unpleasant experience
Now, I don't know the motivations behind why those choices were made. I've heard people (not the designers) say things like "but that's their creative vision, so just get used to it". Here's the thing - I don't care about "creative vision" when that vision inflicts needless pain. It is the height of arrogance - and ego - to say to someone "your real, physical pain is immaterial compared to my creative vision, so put up with it". Torturing a segment of your customers just to satisfy your own ego, is NOT an example of good UI Design or good business practice.
Another argument given is to "just turn your brightness down on your monitor". My monitor is already at the absolute minimum brightness setting. Despite that, simply opening the Windows 10 Settings screen (the Control Panel replacement) still physically feels like I've just been punched in both eyes. I can't turn the screen down any further - there is no lower setting I can use to reduce the physical pain it causes.
Hand in hand with that is the lack of customizability. Given an option, I'd simply alter the system's primary colour themes to dark versions, and everything would be ok then (yes, I know there's a registry hack to switch to a broken dark theme where black titles and buttons appear on almost-black backgrounds, making the dark theme unusable anyway). However, along with the arrogance of believing that their creative vision would be perfect for everyone, was the laziness of not being bothered to provide the ability to modify it if it didn't suit. I've written software myself, and I do understand that it's much easier to just hardcode values rather than provide theming capability...easier, and lazier. It is abysmal that in the chase for "clean and modern UI designs" they have lost view of the fact that it is impossible to create a UI that will be perfect for everyone. Customizability is key to allowing people to adjust the UI to suit themselves. The trend for lack of customization is the modern version of Henry Ford's "you can have any colour you want, so long as it's black" - but with far less excuse for the restriction, and it is just as wrong.
So why don't I just use something else? In the case of Android there is very little else I could use without losing warranty or actual functionality on the phone. I DID used to use a linux phone (with supplier-provided root access!) until it got old and died. I'd still do so now, if the company that produced them hadn't started with this same "one best UI for everyone" nonsense and killed the linux phones entirely. Android is the closest I can get - and for me it's becoming less and less usable as they try to "make it better". The alternatives though are in my opinion even worse. For Windows...I could drop back to Windows 7 - and lose future security updates, and have to come back to Win 10 eventually anyway (only having to pay extra to do so at a later date). My Windows machine is my gaming machine (I use linux for all the others)...and far too many game developers choose to use Windows-only libraries when building their games. This leaves me with the choice of either changing to linux and not being able to play the games I built this computer specifically to be able to play, or having to put up with the physical pain that Microsoft has chosen to inflict as a side effect of their locked, bright-white theme.
Changing to linux isn't a cure-all either...the same kinds of "our creative vision is more important than usability of the interface" has been pretty dominant over the last few years there too. From the introduction of Unity in Ubuntu (no-one ever uses menus so we'll remove them all), to the poor handling of dual screens, or of large screens (I'm using 27"/30" screens at home, and moving window menus to the top bar a LONG way from the window they belong to is silly for a screen of that size). It's been a crap-shoot keeping a functional desktop interface while people designed things that simply interfered with my workflow.
When creative vision inhibits some your customers from using your product, that vision is a failure. When it actually inflicts needless physical pain on your customers, it is worse than just simply being a failure - and if they can't avoid that pain because you've explicitly locked out any ability to customize the interface to remove the source of pain it actually becomes a form of torture. Why any company would want to torture their customers, I don't know...but that seems to be the current consensus outcome of "clean, modern UI design".
There IS and can be NO "one UI to rule them all" - and chasing one is a fools game. Customers all have different preferences/abilities/disabilities, and by locking down any form of customization you're actually reducing the number of people your design will suit.