Question

What is one way employers get employees to participate in a 401k?

by requiring them to participate unless they opt out
by requiring them to opt in if they want to participate
by giving them an annual pay raise
by giving them a signing bonus when they participate

Answer 1

By requiring them to participate unless they opt out — this is called automatic enrollment. Employers who auto-enroll employees (often at a default contribution rate) see much higher participation than opt-in plans.