Beginning about ten years ago, many website providers constructed a separate website for mobile users. Often the mobile website had an address like m.xyz.com or xyz.com/mobile. Sometimes the website server was clever enough to detect accesses from a mobile device and to redirect mobile users to the mobile website. But over time, dedicated websites for mobile users fell out of favor for two reasons. One, it's double the work for a website production crew that's usually stressed out. Two, an ever-increasing percentage of accesses are coming from smartphones and tablets. Those users don't want a second-class website experience, and more importantly the website providers want to serve advertisements to mobile devices.
A smartphone or a tablet doesn't have a mouse. Instead, users select links or hotspots with fingertips. The mouse on a PC turns out to be an extraordinary facile invention, easily capable of selecting 12-point text on a dense web page. Almost no one's fingertip can do that, however. Ease of use from a mobile device means a web page that uses much larger tap zones, such as 1 cm by 1 cm. Hyperlinks in 12-point text are simply inadequate on mobile devices. Futhermore a web page that is dense in the horizontal direction doesn't map well to a small screen on a mobile device, even when the device is placed in landscape orientation. Mobile devices want web pages that are dimensioned like Kate Moss.
Website designers now favor web pages that are intentionally suboptimal for PCs but render reasonably well on mobile devices. If you still use a PC most of the time, as I do, it's frustrating — especially when using a laptop without an external monitor. It's a new curse upon the road warrior. One tip is to use the zoom-out function of your web browser and reduce the web page to 80 or 90% of full size. This will somewhat counteract the large amounts of white space on your PC screen. Another tip is to use as large an external monitor as the graphics card in your desktop or laptop will support. Beware that graphics cards are usually where a manufacturer will avoid costs on inexpensive laptops. Unfortunately the portrait setup for external monitors is rarely seen anymore.
Despite these tips, PC users will just have to live with the unfortunate trend.