As lyx2no pointed out, you have forgotten to include 'time' in your conclusions.
Although you may be correct that every place has been underwater - you have not applied a time-scale.
Every place has been probably been underwater
at some point in time.
The continents of the earth have not always been the same size, shape or position.
Over millions of years the earth's surface changed - some land was slowly raised and some land was slowly lowered.
If land is raised above 'sea level' it becomes dry land and the reverse is true: if land is lowered below 'sea level' it fills with water.
But if land is raised above 'sea level' then it also raises up all the stuff that was underwater (e.g. fossils, rocks, etc.).
(This is a simplistic explanation - but it will do for now.)
I hope this helps.