How is it voluntary if everyone else is pulling crazy hours and you need to keep up (or pull ahead) to stand a chance of making the jump from Intern to Real Emp

How is it voluntary if everyone else is pulling crazy hours and you need to keep up (or pull ahead) to stand a chance of making the jump from Intern to Real Employee? Directly from the article: “Sure, you may not be achieving much by midnight, but do you really want to be one of the first in the team to leave your desk?” George Herbert at PolicyMic asks. “If you’re always the one who leaves first will your boss question your commitment when it comes to calculating your annual bonus or deciding whether to take you onto a regular contract?”