Three of the main reasons were wide screens, mobile devices, and HiDPI. When a layout only needs to work at 640x480 on a 96dpi monitor where you're guaranteed to have a cursor and keyboard a "magazine" layout can work fine.
When a non-trivial number of users have widescreen displays a layout designed for a 4:3 aspect ratio ends up either crowded on one side of the screen or floating in the center with large margins on either side. A layout filling a 16:9 aspect screen will end up being different than the 4:3 layout. This feeds into mobile as well, your 4:3 or 16:9 landscape layout for desktops either looks terrible or is broken on a mobile device in a portrait layout. The graphics that look good at 96dpi start to look shitty on HiDPI screens.
It's entirely possible to make responsive layouts that handle all those cases. CSS and HTML have lots of options for responsive layouts. The main limitation is time/money. It's a lot of work to build a "magazine" layout that is responsive and displays properly on all devices. It's possible just difficult. It's much easier to make a layout that looks equally bland and lifeless across all devices.
When a non-trivial number of users have widescreen displays a layout designed for a 4:3 aspect ratio ends up either crowded on one side of the screen or floating in the center with large margins on either side. A layout filling a 16:9 aspect screen will end up being different than the 4:3 layout. This feeds into mobile as well, your 4:3 or 16:9 landscape layout for desktops either looks terrible or is broken on a mobile device in a portrait layout. The graphics that look good at 96dpi start to look shitty on HiDPI screens.
It's entirely possible to make responsive layouts that handle all those cases. CSS and HTML have lots of options for responsive layouts. The main limitation is time/money. It's a lot of work to build a "magazine" layout that is responsive and displays properly on all devices. It's possible just difficult. It's much easier to make a layout that looks equally bland and lifeless across all devices.