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.


It’s not “companies”, it’spublicly traded companies.
And the answer is quite simple really: the moment you become publicly traded your stock becomes your product, and everything else becomes a means to deliver better stock prices to your investors.
Not all companies are publicly traded, I patronise privately held companies wherever possible because as a client I’m still at the core of their business strategy, and I’m wary of the alternative.
At the end of the day, bad strategies result in bad products and services. Vote with your wallet, it’s very possible.