Don't panic about the initial lack of reviews. I've been dealing with the same thing on my asset collections.
Just keep promoting your asset pack and continue selling... and keep in mind that in general, on most big marketplaces (from Amazon to Steam) usually only 2-5% of customers will rate a thing they bought.
That can be extremely frustrating when you know you have something amazing that's being ignored. But it's reality.
Focus on getting people to look at your work, landing buyers, and impressing those buyers with the quality and value of your product. People who have strong emotional reactions (positive or negative) to your product are most likely to take a moment to review it.
And some people are just inherently more likely to post reviews than others, for whatever reason. Habit, I suppose.
There are venues like eBay where ratings are more standard, and a large percentage of people will leave them. But most marketplaces aren't like that. Itch doesn't seem to be. So don't be surprised if it takes 20, 30, even 50 sales before someone posts a review.