no idea why, more than likely it is a fake review or someone not knowing what they are saing. but i know they do not allow the card to work as intended without full power. some people may get a pc to boot using one of these but i can guarantee the card is not running as it should, despite it booting up. as i noted above, 75w 6-pin can not give 150w of power to a card as the connection desires. at the minimum the lack of power will cause the gpu to look elsewhere for it, which is the pcie slot itself. it can then overdraw that slot and damage the mobo.
at the worst, the card tries to pull the full power from the adapter and melts down the circuit causing a nice cozy fire to roast marshmallows to. neither is a good result. you need a new psu or a different card.
for instance a 1650 super only uses a 6-pin and is a lot stronger than a 570 as well. a regular 1650 usually needs no extra power at all. there are plenty of good options that only use a 6-pin. just see what else is available that your psu can actually power.
also note that most 570 cards don't use an 8-pin either. no idea what model you are looking at but look at others as only the top end overclocked models would need extra power. do look again and you might be mistaken about the 8-pin need. now if you actually meant an rx 580, then yah they all need an 8-pin.