Too many people it seems to me only hear part of the words of the verse or misinterpret what they do hear. It says "humble themselves". It does not say for us to presume that God will be there simply because we have been called by Him. Being called, we must continue to listen to His voice and to call upon His name.
Many really are called, but if we do not answer Him each time and calls and obey Him, should we expect forgiveness for our sins or healing for our land?
Consider what is written a few verses later in the same chapter:
"But if ye turn away, and forsake my statutes and my commandments, which I have set before you, and shall go and serve other gods, and worship them;
Then will I pluck them up by the roots out of my land which I have given them; and this house, which I have sanctified for my name, will I cast out of my sight, and will make it to be a proverb and a byword among all nations.
And this house, which is high, shall be an astonishment to every one that passeth by it; so that he shall say, Why hath the LORD done thus unto this land, and unto this house?" II Chron 7:19-21