Why do some companies stop growing?

After years of steady and significant growth, at 10% or even 15% per year over 15 or 20 years, some companies stop growing. This has a major impact. For example, a company that used to grow at 10% per year over a long period and then suddenly stops growing sees its PER1 drop from 30x to 10x – in the current low-rate environment.  

One might think that such an evolution is inevitable. But it is not.

What are the usual reasons for such a slowdown?