There are, of course, many reasons why your website should be mobile friendly, but in my opinion there is only one reason why you need a mobile friendly website and why you should be worried if it is not.
If you do a Google search for “why do I need a mobile friendly website?” you’ll be presented with a list of websites that give “3 reasons why you must have a mobile friendly website,” “10 reasons to make your website mobile friendly,” “Five compelling reasons you need a mobile friendly website” and so on.
While all the reasons they give are valid, they all amount to the same thing.