What demon do I need to sell my soul to for some Amazon ads???

I got selected for a Book Bub promotion and it went pretty well, I thought - around 500 downloads. I thought for sure I’d get at least a couple dozen reviews out of it, but so far I’ve gotten maybe 5 new reviews. Is this normal? Does it just take a while? More importantly, is there a better way? The reviews I’ve gotten are pretty overwhelmingly positive. I just need more! Has anyone found anything that really works?