Post it on game dev forums outside of itch? There are also other asset specific websites. idk if they have any more or less traffic than itch. Oh... start a YouTube channel to hype them?
I've released some free art asset packs. Probably sub-par compared to what others are doing for free, but they always seem to have a lot of views per day and a few downloads per day. I haven't bothered to promote them, people just find them.
Another issue could be over saturation. Your new art has to compete with all the 5 stars of assets from 5+ years ago. Unless you have a following, good luck finding them on any website.