They managed to accumulate wealth through Business by utilizing education and skills, a successful career can take them to a level of Financial success. What these people have done proves that without investment they can accumulate huge amounts of wealth, even exceeding the value obtained from investments in general.
The purpose of investment is to help increase wealth and achieve long-term financial goals. Some people who have achieved success in business will allocate some of their money to invest. This can benefit them when income from other sources is disrupted.
For some people who have big businesses, they can indeed become rich without investing, but what needs to be considered is that only some people are like that and many people also achieve wealth by setting aside some of their income and starting to invest, it will have a big impact in the future.
The purpose of investment for people who are already rich is to increase wealth as you said, but the rest of the people don't think that way, in fact many people start investing to achieve wealth in the future, so I think people need to invest if they want to be rich.