Short answer: WordPress can be used for any business, no matter its size. It can be customized for a variety of different needs.
Long answer: Is there no real reason to say WordPress can only be used for small or midsize websites. Although it excels at that, various websites around the world use WordPress, including major corporations, online shopping websites, eCommerce or digital marketing, etc. Some of the major websites that are powered with WordPress are TechCrunch, The New Yorker magazine, Time Magazine, cPanel, Playstation, and many more.
