Edit: This question attracted way more interest than I hoped for! I will need some time to go through the comments in the next days, thanks for your efforts everyone. One thing I could grasp from the answers already - it seems to be complicated. There is no one fits all answer.
Under capitalism, it seems companies always need to grow bigger. Why can’t they just say, okay, we have 100 employees and produce a nice product for a specific market and that’s fine?
Or is this only a US megacorp thing where they need to grow to satisfy their shareholders?
Let’s ignore that most of the times the small companies get bought by the large ones.
Extremely oversimplified:
-for Public Companies: CEO and executives are obliged to pursue maximum profit (either short-term or long-term) for the shareholders, thus the company must grow. - - For shareholders its Cost of capital (basically shareholders want bigger returns than the investment they made) and Opportunity Cost (lose money because you don’t move your investment to a company that is more profitable or gonna be more profitable)
-for private companies: Competition (grow or die from your competitor), efficiency (reducing cost), exit (sell it big and retire), psychological reasons (better safe than sorry), etc…
There are many family business or small companies that function as you describe, but they get replaced and driven out of business in a matter of years or decades (with exceptions). But being stable in an growing economy is very hard and risky. And Capitalism by definition must grow or it gets in crisis.