Hussar
Legend
There's no way in heck that "most" characters are multi-classed. Their data is biased in favor of characters that require an online tool to build, and away from the normal characters that we write down by hand.
I dunno, it certainly dovetails with my experience.
Of our five now 5e campaigns, so, about 30 characters (or so), there have been vanishingly small numbers of single classed characters and by far the second class has been fighter. To the point where I've only seen one or two single classed fighters out of about ten or fifteen characters with fighter levels.