Lots of them are offering a gift card for a review to purchasers - which seems slightly less scammy as you’re unlikely to leave a good review of a crappy product for a $5 gift card.

I had this happen, left a negative review mentioning the pay-for-review scam, and had the review removed by Amazon because it's "off topic". I don't know if it's just aligned incentives, but Amazon doesn't seem to care about this kind of review stuffing at all.

All the gift card offers I have gotten have required a 5* review.

Sure - but you’re less likely to want to leave a five star review if the product pissed you off.