And sometimes it really is a technical issue. There was a time when every "grey" sweatshirt was impossible to find. This was a glitch that occurred almost throughout most of 2018 and part of 2019. If people searched "grey sweatshirt" they could find them fine. But if the seller didn't use the word "grey" in their title, and only selected the "grey" in the color category, the search engine couldn't locate them. So, again, glitches do occur.
As for slow sales in the past couple months, even eBay is aware of this. For whatever larger reason, general sales for March and April of 2021 have dropped dramatically. I wouldn't be surprised if the same is the case for Amazon sellers. My sales in March and April have devolved to about the same rate as March and April of 2016, when I had a much smaller inventory.
