Don’t confuse design trends with functional improvements. RWD means for most web developers that the horizontal scrollbar doesn’t ever need to appear. Which is just someone getting their jollies off media queries.
(“real” responsive design works on the idea of sending the least amount of BS to anything with a mouse-turd-sized screen, because unless we can measure, we’re assuming mouse-turd screens are running on batteries, have crappy low-power CPUs, and are attached to crappy networks and slow speeds and lots of outages… so images, scripts, fonts and other garbage need close regulation. However, this seems to not be the case with most sites claiming to be “responsive”-- instead, they just mean the web page is squishy when you shrink your browser window)
The design you’re talking about is a combination of Apple styles, Microsoft Metro’s “flat” styles (not that they invented it, but they popularised it), and nowadays it’s Google’s Material design, which mostly appears to be an overuse of SVGs and the Metro “flat” look but then with super-subtle drop shadows that half your users will probably miss anyways, combined with a strange belief that people need flat interfaces to appear more 3D, despite the fact that they still feel pretty flat to the touch, rendering the whole idea a bit moot…
Also a “minimalist” blog style has been going around, popularised by a couple of Turdpress themes (thanks deathshadow for that term), and more recently by sites like Medium.com. These are mostly a large header image followed by a single column of large, readable text. I believe some of us know that large header image as the “12MB image of someone smiling at a salad” as described in a tweet by @wilto.
I’ll argue with you about the large readable text and even the kindergarten buttons-- users with crappy eyes and crappy motorics are so happy they finally have text they can actually read (instead of that 11px Arial crap designers have been foisting on us all these years) and buttons we can mostly hit even if we’re kinda sh*tty using pointing devices (the bright candy colours and the flat “unclickable” look are another matter).
…though I do know of one visual impairment that does worse with larger text, that being where your vision is restricted by a “tunnel”, or peripheral vision is low. In those cases, larger text can make it difficult for the user to see an entire word if it’s somewhat long.
So mostly what you’re seeing is what we call a “trend”. Responsive design as it is right now might also be a trend the way WAP sites were, but the idea of a design that doesn’t care too much about screensize is probably going to stick around, and not really worth hating since it gets rid of (usually painful) horizontal scrolling thing.