There were warnings given to the Titanic prior to striking the iceberg by a nearby ship the Californian. The responce was "Shut up, shut up, I am busy; I am working Cape Race". http://www.titanic-titanic.com/collision.shtml
http://www.titanicinquiry.org/USInq/AmInq08EvansCF01.php
This world is in a similar situation. People are busy, overconfident, and skeptical. You never know when someone might soften their heart and listen, so we keep going to their doors.
(2 Timothy 3:1-4) But know this, that in the last days critical times hard to deal with will be here. 2 For men will be lovers of themselves, lovers of money, boastful, haughty, blasphemers, disobedient to parents, unthankful, disloyal, 3 having no natural affection, not open to any agreement, slanderers, without self-control, fierce, without love of goodness, 4 betrayers, headstrong, puffed up with pride, lovers of pleasures rather than lovers of God,
(Matthew 24:14) And this good news of the Kingdom will be preached in all the inhabited earth for a witness to all the nations, and then the end will come.
(Matthew 28:19, 20) Go, therefore, and make disciples of people of all the nations, baptizing them in the name of the Father and of the Son and of the holy spirit, 20 teaching them to observe all the things I have commanded you. And look! I am with you all the days until the conclusion of the system of things.”
(1 Timothy 4:16) Pay constant attention to yourself and to your teaching. Persevere in these things, for by doing this you will save both yourself and those who listen to you.