If you believe your origin and your destiny are agent-less and meaningless, then it makes the most sense to call everything in the middle meaningless also. Thus - eat, drink, watch TV, have fun till it's over. I can see that making sense.
But if life and its pursuits have any shred of meaning, then I think it's OK to say they could be doing better things with their time.
For some reason, though, there are a shitload of people out there that don't have this ambition. I understand difficulty empathizing with it, because to people like you and me it does look like a "waste of time." But for some reason it really is just ideal for a lot of people to be able to switch their brain off and sit comfortably in front of a TV and be entertained.
For these people, you could argue "you should be doing something better with your time," but all you'd get back is "why? This is comfortable."
Just as my life is not for them, their life is not for me. At least they have some way to entertain themselves, whereas every second I spend relaxing comes with anxiety over whether I'm spending my time "usefully."