Employees often keep working in organizations that they are unhappy with. Reasons include financial pressure, like student loans or a mortgage.

Providing interesting or a variety of projects keeps talented employees on board.

Innovative projects eventually reduce the need for old software/old processes that are normally active for decades as no one is capable or interested in providing a more efficient way to work.

• Respecting employees, and recognizing their good work goes a long way in retaining them.
• Employees that are rewarded, respected and recognized develop job satisfaction in their organization.
• Subtle things including a kind action or an appreciation also form a positive mindset...

A short-term fix for making employees stay is to pay the employees well. This is not a long-term strategy, as having people in a company for purely financial reasons wouldn't be a good idea. But if employees aren't paid well, great performers will find it hard to stay.