Is selling Ui Kits in 2020 still Viable?

Hello guys, I need your help.

I want to ask designers who do sell UI kits or have some experience with selling, buying, or using UI kits.
Note: this is not a post to promote my products in any way.

I’m Raouf, a UI designer who Builds Figma Ui Kits to help designers and non-designers build websites faster with Figma.
UI kit At :https://figmaland.com/uikit/ui-max

Now, this is my problem: I am struggling to sell my Ui Kits. I tried several methods without success.

I tried to share my UI kits on popular platforms like ui8 and Uplabs. People are buying and appreciate my products on those platforms, but in less than 24hours, my kits will disappear in the sea of other newly posted UI kits. and show no more download the next days.

To be proactive, I started giving a free version and charging for a premium version of a UI kit. I reached more than 440 free downloads and just one

I tried building a newsletter and gathered more than 200 emails, but got almost 0 buyers converting from the mailing list.

I tried a Producthunt campaign, got more traffic to my website but it didn't convert.

I tried content marketing on medium too, and give away lots of free design freebies.

It's been three months now of working regularly on creating and promoting UI kits without getting results.

The ideal is to sell my products on my website without depending on a marketplace.

Until now, I just sold one Ui Kit on my website.

1 - Is it the fact that my UI kits are exclusively for Figma users?

2 - Maybe the pricing, which is 99$

3 - Am I miss understanding the market of UI Kits? If so, based on your experience, who are the potential buyers of UI kits?

Thank you guys for your help. It will be really helpful for me and other designers, who are facing the same case.