Such is life: "I am better than you because....."
Whether that's the car that you drive, your lifestyle choices, the colour of your skin or how many reviews you submit.
It is what it is, if there are 1000 users and 10 submit regular reviews on a free site, just use the reviews, the non reviewing 990 take nothing away from that, they don't make your experience any worse, perhaps it's better if they do review, but is forcing somebody to review against their will or creating false reviews just to have boxes ticked, is that better? There's always the chance that some "leech" who's been doing some nervous research before taking the plunge will start posting reviews a year after joining.