Ah, for ye olden days of the Internet — when a designer could build a website to a particular fixed width that would likely fit on any common display. One and done.
And then along came smartphones, and the concept that any one design would suit all of your website's visitors went entirely out the window.
After a brief and misguided fix that involved creating entirely separate sites designed to be used by mobile visitors — Who remembers those "Click here for our mobile site" links? — industry best practices landed on a much better solution: responsive design.