Recent actions by the IRS are giving folks haste to resolve their tax problems in late 2018. Non-filers of 1040s are getting notices asking for their 2014 thru 2016 returns. Failure to comply results in a possible Substitute for Return created by IRS for you and not in your best interest. Also, for people with $50,000 plus tax debts, letters are going out warning of possible passport revocation, but more likely passport renewal denial.
IRS actions are seasonal and unpredictable, of course. But clearly they are ramping up collections again. Revenue Officers are also getting assigned to big dollar cases as well. Recent tax cuts are drying up the coffers so not a huge surprise. (IRS could re-brand themselves as the Deficit Reduction Organization (DRO) and maybe de-politicize the place, getting it back to it's old fundamentals: collecting taxes to pay for government services and reducing the debt.)
Non-filers should think carefully before filing ten returns. Passport holders usually can get their case resolved thru Offer in Compromise or livable payment plan and their passport revocation threats reversed.