2. Fear of going to jail? We find that fear of going to jail as a big catalyst of people to take action although the IRS is probably less inclined to jail you for non-filing in 2016 then in any day in its history (budget-cuts).
3. Getting a passport? Immigration and the IRS are working together more closely in recency- Passport Revocation News. Not filing a tax return and owing taxes can put restrictions on overseas travel more so then it did in the past.
4. Self-interest? Well if you count #2 and #3 above, self-interest and self-preservation do rule the day. And if you are self-employed, filing back taxes and then settling with the IRS might ALSO have a big net positive effect: increasing your social security benefits at a dramatic discount (!).