500watt is not 'low watts'...
Because of several years of marketing brainwashing, astroturfing , misinformation and people justfifying their 150+ euro 1000watt psu purchases changing people's perspective on how much power their pc consumes and how big a power supply they need.
At others asking: again, people were running gtx 260s (180watt tdp) and power hungry i7 920/960s (130watt lol, massive compared to modern i5/i7s) on 350 watt power supplies for years without issues.
A few years ago it was especially bad, tons of people replacing their perfectly fine 450-550 watt psus with 750+watt ones just because they were buying some 200watt tdp gpu...