The context of this conversation is full-time salaried employees who give more than they financially get, so personal satisfaction, influencing others' behavior, or prestige at the company are some potential answers to your question.

A lot of (most?) tech industry workers change jobs every 2-3 years and develop no particular attachment to or long-term plans for remaining at a company.

Thanks for the answer. Having had experience with both employee and contractor colleagues (and having been both) I'd say the only one that might not apply (but also could, depending on circumstances) to contractors is prestige at the company.