At busy times I agree that people should not sit around and play cards but I do have an issue where someone feels they have to "dine and dash". Where they wolf down their food and then get the heck out of the lido to free up the space.
I have also found that if you go to the "out of the way" spots at the rear of the lido or even outside you can usually find a space. If not I just ask someone if they mind if I, and usually my wife, share the table. I think I've only been told "no" once.