This is an acronym for "Due To Lack Of Interest." The term is popular as a sidebar or casual comment about why something did or did not happen, regarding events in business or personal life. When said out loud the correct method is to name each letter (like this: dee-tee-el-oh-eye), not turn it into a spoken word. Often the term is used in a snarky way.
Two examples:
"The project meeting today is canceled, DTLOI."
"I told her I could not be a bridesmaid in her wedding because we were going to be hiking in Afghanistan that month, but truthfully it's just DTLOI."