Most "mobile" versions of web sites are objectively worse than their "desktop" versions.
Actual advantages of mobile devices are:
* High DPI, handheld. You can look at a mobile screen from different distances for different use cases and screen contents.
* Less eye movement required than for using a typical HD desktop monitor. This makes it easier to navigate unknown applications / web sites.
* Easier to tap anywhere than to click anywhere with a mouse.
* 360° scrolling with high accuracy and intuitive control over the velocity.
* Zooming with quick and intuitive gestures.
Mobile devices are perfect for navigating wide, complex web sites. That's why "mobile" versions that ignore the advantages of mobile devices are usually worse than the desktop versions.
How "mobile-optimized" apps / web sites often fail:
* Overly large elements and fonts that cannot be zoomed out from. High DPI goes to waste.
* Fixed elements that obscure parts of the screen. They make the scrollable area so tiny that you have to move your eye balls quickly when scrolling.
* Hiding important elements in hamburger menus or making them inaccessible. Finding stuff has to require multiple taps so that it is even slower than with a mouse.
* Horizontal scrolling is evil except in awfully implemented code snippets. It is unimaginable to the modern web developer that someone would double-tap a column of text to read it and scroll around afterwards to discover what else the site has to offer.
* Vertical scrolling is too hard even though a touchscreen is perfect for that. All the "important" shit has to be fixed because users would be too stupid to find the menu by scrolling. A fixed "back to top" button is the icing on the modern web cake.
* Zooming is too hard so it should be better disabled, bugged or useless.