For some, it probably fell on deaf ears. Time passes. People fall into a day-to-day world. Current matters are more pressing and need to be attended to. The focus on a return becomes remote. Doubters soon replace the faithful. God is not so omnipotent as they once believed. Everyone is still here and doing the same old things.
What has happened? It's been hundreds of years since this promise to return. There's no big event. God begins to change. Not really, we change how we think about God. "For I am the Lord, I change not; therefore ye sons of Jacob are not consumed." (Malachi 3:6)
How easy it is to forget that the world was spoken into existence and out of it by the word of God. Second Peter 3:5-6 says so. Peter goes on to say in verse 8 that one day with the Lord is as a thousand years and a thousand years as one day. It says much the same thing in Psalm 90:4. In one day, God can do the work of a thousand years!
When God returns, He will be here. It says in the Bible that it'll be like a thief in the night. All of a sudden, GOD IS HERE! The warning of His return was made a long time ago. Be ready. Like Pastor Josh said in an evening sermon covering II Peter 3:9-13, "Plan for the forever--not for the now."