In the early days of computers and the internet, there were just desktop PCs and slightly smaller laptops. And in the REALLY early days, you were limited to 800 pixels across of screen size (in the “Y2K” era).
Over time, monitors got larger, screen resolution improved, and sites were adjusted to 100 pixels, 1200 pixels, 1600 pixels and even larger. Over time, internet speeds got faster, too, which meant images could be larger, and video can be streamed without adversely affect many users download experience.
The smartphones were invented. First the Blackberry, then the iPhone, followed by a virtual tsunami of Android and Microsoft Windows versions. These had smaller screens (as narrow as 320 pixels across, but were colour and allowed full internet functionality, unlike the texting-only capability of the phones that preceding them.
Web interfaces need to be greatly abbreviated to fit onto smaller screens. and interfaces need to be touch-screen compatible, with large clickable buttons.
In the early days of smartphones, many companies developed “apps” that used each device’s special capabilities. But with the device proliferation, creating multiple apps was more efficiently superceded by mobile web interfaces, using the browsers that ran on each device.
And over time smartphone screens got larger and larger ot display more information. When Facebook offered a smartphone version (as an “app”) a new metaphor for smartphone content evolved: the scrolling page that went on forever (or until the user got bored or ran out of time). On the desktop, Pinterest had a similar design metaphor: a waterfall of content that users can scroll down forever, to view more content.
When tablets–with only a touch screen interface–were invented, they filled a middle ground: screen sized like a laptop but no keyboard, and a touchscreen interface like smartphone.And you can hold it “tall” like a book, or turn it “wide” like a television or movie screen. Most accessed the internet through a fast WiFi connection.
Instantly, users demanded larger images, better interfaces, and the smartphone/desktop interface divide was out the window. Responsive design was “in”.