Because I'm not mister money bags mate. Saw good deal and took it, but here's a thing. I also was willing to modify my card's vBIOS to my liking and now it's capped to 100 watts and 1100 MHz core clock. In practice, actual power consumption of card varies and is 70-90 watts in gaming. With such tune, I can only reach 100 watt power usage in very specific mining or distributed computing situations, maybe in Furmark too. Also my specific card wasn't 180 watts, it's 145 watt card from factory and in most conditions actually only consumed 130-140 watts. Why that happens? Because card hits clock speed, voltage wall and games don't utilize GPU resources ideally ever. Also you didn't really know that Polaris cards are phenomenal undervolters, I tried that out, but didn't stick with it. There are good gains, but alone weren't good enough for me. So I ended up with card, that is faster than RX 570, but slower than RX 480, while consuming less power than GTX 1060 and is slightly slower than GTX 1060, but performance per watt is higher. So, yeah I'm fucking menace of free market and of reasonable cards. Anyway, where I live, RX 580 which I bought was selling for 210 Euros new, meanwhile GTX 1060 6GB was going for over 300 Euros. As you see, I don't like to be robbed by Jen-chan and took proper action against that. Unfortunately, AMD clamped down on vBIOS modifications and now you can't do it in reasonable way anymore, so next time I will care about official wattage rating much more and next time I won't buy lowest end model of card either.
Edit:
A bit off-topic, but my whole PC with CPU and GPU mining at same time, uses only 230 watts or less. In gaming it uses 170-210 watts. I think I managed to reach 250-260 watts with prime95 small FFTs and Furmark at same time. At idle it sips 45-50 watts. When turned off, it consumes 0.2 watts. Come on dude, your i9 uses more power than my whole PC, you have some audacity to knock on its power usage.