If the pool opens at 0700, the staff should remove anything that is on a chaise before 0700 .
After that, I believe staff should be removing things routinely, especially if no one is in the water.
If they have gone for a meal, too bad....last cruise, we went one at a time, and brought our Waves or Terrace meal back to our pool chaise. Not the most comfortable way to eat, but if you're serious about wanting a place to relax, c'est la vie!
I DO think it's the cruise line's job to monitor this.