Explain Like I'm 5 (ELI5)

Why can’t I, in theory, start a business, grow it until it’s successful, then just…be content and stop growing?

I mean you could, there's millions of (usually small) businesses that do this, they may be like cafe's or something like this that can only reasonably reach the population in the physical area around them

A lot of businesses are just looking to make enough income for those who work at it and if it's a 2 person job then if they're making enough some may knock back work to balance their lives better

You could also operate a non-profit organisation: https://en.wikipedia.org/wiki/Nonprofit_organization

Why do people talk about it as inherent to the system to grow like cancer? What about capitalism causes that and why can’t we avoid it? Like, technically speaking?

A significant amount of Lemmy users are American and poor

Like many Dickfingers supporters they cannot accept their situation is because of them, so while Dickfingers fans blame socialism, the elites, WEF, jews, etcetc for their problems left wing people blame capitalism, the elites, WEF, jews, etcetc for their problems

Both are forms of external locus of control, where people believe outside forces rather than their own actions determine their fate. This can be a psychological defence mechanism to manage stress or cognitive dissonance.

https://en.wikipedia.org/wiki/Locus_of_control

Take everything they say about economics here with a grain of salt