We have 30 year old ceramic tiles on a cement floor . Seaside location. Mild climate, no freezing, no air conditioning (sea breeze through open windows).
A few popped up 5 years ago. Now quite a few more have done this. After we had removed the first lot, suddenly in front of us several more popped up. The builder showed us that the scree under the tiles was of a very poor powdery quality. Is that the whole explanation; a poor job the first time around?

More along the lines of techniques and products have improved during those 30 years. There would be something like a Schluter system on that cement floor. I have a foyer of ceramic laid in a 2"bed of mortar, they don't do that any more either with better and cheaper products available. http://www.schluter.com/intro.aspx