Youtube for Instance has changed it's layout to try and reserve horizontal space so it's "compatible with mobiles". But the thing is, there's a Youtube app for phones and has nothing to do with the PC site ! And when you open Youtube with a browser app, you still get a separate mobile interface. What were they thinking? It's like the design team had no idea about the mobile app.
There's a saying,
"if it ain't broken, don't fix it",a thing that many companies don't understand and often end up breaking their software.
All in all modern UI's provide very little customization and move stuff that was cemented in our brains for years and make them ten menus away and are designed around a "one for all" philosophy that only panders towards the devices they're broadening to and has a negative effect on users of the original hardware it was made for, which can easily be resolved by making separate interfaces for devices.