Why would any owner sell their company to Warren Buffett / Berkshire Hathaway?

You are assuming too many things.

Quite a few well run companies due to various factors are in liquidity crisis. If not resolved, they would go bankrupt. So they approach Warren and quite a few Private equity firms. A deal is made.

Most of Warren investment are also through regular purchase on stock market via block deals.

In the example you have quoted, if the company doesn't need additional capital, it will not sell. If it needs additional capital it will consider the offer.

Let's say you are offered ten million dollars.

You have the choice between taking ten million dollars, and spend the rest of your life on some lovely beach.

Or you can keep working hard until your company is worth twenty million dollars. You could still go to a lovely beach, but you missed many years of beach life, and you are now old and exhausted.

Which one do you choose?

(I know a young man who lives in Malta now with his lovely wife, and who has about £60 million to spend. He's a lovely guy, quite normal except that he has lot of cash. Why would he go on working? )

Another reason someone might sell out: They are equity-rich but cash-poor. If they're running their company well, Warren Buffett isn't going to mess with that — they keep their de-facto position but get a pile of cash.

Because Warren Buffett knows something you don't know. Also you may be a dummy and call from him is not an indication of how well your company is doing.

As an owner you can estimate answers to this questions:

• How much money I can earn in the next 10-20 years
• How much money I can loose in the next 10-20 years

and Buffett can either:

• make more money than you think you are able to earn. Simply because you don't have R&D funds and/or development money
• Loose more money than you think your company is able to. Because, believe it or not, people are buying companies to lose money on them because then they can deduct more money on "loss" side and therefore earn more money by paying lower tax (in general simplification).

And most important: People don't like waiting for gratification. You gonna earn 10 millions during those 10 years? Buffett is giving you 5 millions on the spot. No waiting. Not in five years. Right here. An individual looks different on theirs personal income than people who calculate income in matters of years if not decades.

You think you can spend one million on drugs and hookers and then live forever on interest form remaining 4. Because that what YOU personally need.
Buffett have those "comfy money" for years. And I cannot say why multimillionaires want to have more millions.

Suppose that I'm either an owner or part owner (through shares) of Example Corporation.

why would any owner want to sell a profitable, well-run business that's likely to be around to give returns well into the foreseeable future?

A modified version of gnasher729's answer: because, after 30 years of 70 hour weeks, the owner wants to relax. He couldn't watch his children grow up; maybe he'll see his grandchildren grow up.

Or... he's getting divorced and doesn't want his wife to have access to it. Better to sell the company and give her cash.

There could be 101 different reasons why someone would sell out their company. Some examples I have heard Buffett say over the years include:

1. It is a private family owned company, and the company doesn't have anyone in the family who wants/ is willing to take over once the current leader passes away. So they sell it, take the profit, invest in something passive for the family. Instead of selling out to their competitor.

2. Being a C level executive of a publicly traded company is a giant pain. You have to spend a lot of time justifying everything you do, raising capital, watching what you say etc. When you get bought out by Berkshire, Warren tends to be easier to deal with then a lot public investors. Warren is also notorious for staying out of your hair until he sees something that he doesn't like. You have more time to focus on the business, even if you own less of the company.

3. The company could be a gold mine, but has some bad management, and is undervalued because of the management. Buffett sees that and puts someone more competent in charge, the stock goes up he sells.

4. He liked the company so much he decided to buy it, and put you back in charge to run the company with a good compensation that takes away your exposure to the market. Good stable pay can be valuable to.

5. You bought the company when it was doing badly, you turned it around, the stock is much higher, and you have a large equity position, but no longer want to be in charge of the company. You want to move onto the next bad company so you can turn it for a profit. You find a suitable replacement, and sell out your position in the company to someone like Warren. You get your payday, he gets a good company.

I am sure there are more, some of them have been mentioned in this thread.

RISK. BH is taking on risk, and alleviating risk to you, as owner. Risk comes with a cost. On the buy sell, one will offer less if the risk is high. On the sell side, one will accept less if the risk is high.

Each other's risk assessment, AND risk value will be different. Longer the time horizon results in exponential increase in risk.