Millions of businesses are using shared hosting to serve their website but many of them get kicked out of their hosting company for using too many server resources. On any shared server, the resources such as CPU, memory & disk IO are shared among all users hosted on that server thus if one user starts using all the resources, it may cause slowness for all other accounts on the same server. Ideally shared hosting should not work but with some monitoring tools, web hosting companies are able to detect abusers and suspend their hosting account to protect resources for other users.
So while, most of the businesses do not use high number of resources, there can be a few who do, and those who have plain simple website may also end up being suspended, reason could be a DDos attack or scrapping or brute-force or someone making too many requests in a short time period. While moving to a VPS or dedicated is easy, its a little difficult to decide which one will be apt for the situation.
While a Virtual Private Server can serve thousands of resources every minute, it may also fail if not properly configured, thus making the website to be moved to a dedicated machine. Is an expensive Dedicated machine or a cloud hosting services really the workaround or can a VPS be able to handle a huge resource demand.