Developers are the most sought-after resource in IT, so large companies often offer them an option program along with their salary. This is when, after some time, the employee gets an opportunity to buy shares in the company at a fixed price, usually below the market price. This is generally very profitable. And so. A developer gets a job at such a company, they work off as long as they need to in order to obtain the highest possible conditions under the stock option program. As a rule, this is 1 year of cliff + 4 years of vesting. I'm not going to talk about cliff and vesting. To make a long story short, you have to work for 5 years. Immediately after that, the developer leaves for another company for the next option. Over a career of 20-25 years, the developer will get the most out of each company. So they diversify his retirement with stocks in the companies they worked for.