Originally Posted by
Spider-Chan
New characters always have a hard time. Especially with the current distribution system. I would also question wether Ultimate Jess is as popular as those other two. She has never had a solo ongoing, and you don't really see much of her outside of niche Ultimate universe fans.
I would say that each one has different reasons about why they didn't catch on. I would definitely say that being directly connected to Peter automatically gives you higher chances. The likes of Jessica, Julia and Anya weren't exactly connected to Spider-Man. Heck, they didn't even debuted in a Spider-Man issue.
I would say, lack synergy. Synergy nowadays is a very big factor. I'm not talking about movie/tv/comic synergy, but a character making multiple appearances in different books. That will ultimately lead readers know more of them and be interested in their other stuff. Mayday was THE face of the MC2, she was practically showing up everywhere in that line. Gwen has also got into guest star in various other comics (despite living in a different universe), as well as had a entire month dedicated to her. Or just look at some current characters, like Cho!Hulk, Kamala, Nova, Laura, Moon Girl who get guest appearances in various comics.
Compare to Anya, who, after Araña ended, ended up in Ms. Marvel of all places. She never appeared in a Spider-Man comic until Grim Hunt, a event that was more of a turn-off than anything else. Once she became Spider-Girl, she once again practically didn't appear in any issue of TASM or any other A-list title outside of a back-up story and the occasional background cameo until Spider-Verse. I always wonder what could have been if she would have been part of the relaunched Captain Marvel cast. Kelly Sue Deconnick wanted her in CM, but editorial denied her to use her, despite Anya being in limbo during (and after) that time. That comic alone spun-off the new Ms. Marvel and Spider-Woman (yes, I consider that last part true since KSD was using Jess more than any other writer at the time in CM and Assemble and lead fans being introduced to her to see her in a ongoing).
Silk is a case that she originally did had a hype behind her, having debuting and being a key character to a Spider-Man event. After that, she didn't really appeared in any other series outside of her own.
If a character gets a push in other comics, guest starring or being part of more a-list titles, the character will have a better chance. Readers would say "hey, I like this character, where can I read of them?" and be directed to their respective ongoings. If a character is practically isolated from the rest of the universe, they will more likely be ignored.