That is one philosophy:
* https://en.wikipedia.org/wiki/Friedman_doctrine
* https://en.wikipedia.org/wiki/Shareholder_primacy
It is not the only one:
* https://en.wikipedia.org/wiki/Stakeholder_theory
* https://corpgov.law.harvard.edu/2012/06/26/the-shareholder-v...
They do not actually.
* https://archive.ph/VCUp4 / https://www.ft.com/content/7bd1b20a-879b-11e5-90de-f44762bf9...
* https://www.pqmagazine.com/the-myth-of-shareholder-ownership...
* https://www.forbes.com/sites/petergeorgescu/2021/07/21/the-s...
* https://edwardslaw.ca/blog/shareholders-agreements-in-canada...
* https://www.ippr.org/articles/who-owns-a-company
* https://www.cambridge.org/core/journals/journal-of-instituti...
They have certain claims, but so do customers, suppliers, employees, governments (taxes), bond holders, etc. The claims of shareholders come last, which is why owning stock gets you higher returns (than, e.g., bonds from the company): you're at highest risk of losing money from being last on claims, so you should be rewarded for that higher risk.
Having IOUs from the company in the form of future goods or services owed to customers, interest payments owed to debtholders or future taxes owed to the government do not equate to having an actual ownership in the business.