Eventually, the owners are gonna want to retire or they will die. Maybe, the business can be inherited or passed on to family, or an employee. But if your family doesn't want to take it over and you don't have any employees who are able to run it (if it is profitable enough you could consider hiring a manager), you either sell or shut down. Generally, most find it preferential to sell. And most who have spent their life working on something would prefer to sell and use the income to fund their retirement- and see the business continue.

There are lots of different exit strategies, but oftentimes a sell of some sort is the only one that really makes sense.