Should a businesses goal not be to tighten their hold on the market? I’m pretty sure if I don’t, someone else will.
However, the owners of the company are humans that do not need to be constrained by those rules. Indeed, humans can hold other values higher - such as seeing that acting in the benefit of the entire society or even to benefit the entire planet is better than focusing on the best for a single corporation.
Pretend for a while that you are the majority owner of an internet company that preys on attention. You can capture the attention of millions, even billions of humans, and grow your vast empire. You can even become so successful that humans choose your product before the attention of other humans, choosing the dopamin kick from social media before real social interactions.
But...should you? Replacing the social interactions of an entire planet might make you rich today, but the price might be very high. Even your own offspring might suffer and perish in a world where social life has been replaced by hearts, thumbs up and endless scrolling.
That's a 2020 benefit to an entire society that arose from 25 years of effort to grow in a sustainable way.
Ingvar Kamprad net worth was "only" 3 billion $
That's about 25 billion $ lower than if he had unfettered access to all of IKEA's worth.
https://www.forbes.com/profile/ingvar-kamprad/
If you like how the company you built spends money more than how the state spends money, you're going to want your company to capture more money/worth without relinquishing it to the public. Another rationale could also be when you can give a stake in your company to your family, that way you won't ever have need to pay profits during your lifetime, since the company (which could be a charity) will actually work as a cross-generational fund.
Also, this works well with the ethos of some companies (like Amazon, allegedly) which reinvest a lot of their profits to cut margins/develop new products... And overall just tighten their hold on the market