Based on lurking and observation on places like reddit and twitter, I think a key factor that makes Chainsaw more liked is that it is easier to read and follow and the readers don't have to spend 5+ minutes looking at a wiki or asking someone what something means. There's tons of times where I've seen people forget what in-universe terms mean and I think the effort required to read or keep up is part of why I think Jujutsu doesn't have the same readership as Chainsaw. I could just be generalizing, but it seems most western manga readers like easy to read manga that doesn't use confusing/hard to remember terms, which many have said is a part of why Sam8 failed because no one cares about dozens of words/phrases that mean nothing to them.
Chainsaw has messy art, but the line work in general is still smoother and more clear than Jujutsu and therefore easier to parse. Both series have good depth with the tones and such compared to early Sam8, but I think the messy art in action from Jujutsu detracts from the experience from some readers I've seen in comments, where they say they can't tell what is happening.
Same thing people said about Kimetsu when it was less popular, people can't be bothered to try and parse "ugly" art, so they just assume it is a bad manga and don't read it unless it gets popular with an anime. I don't know how popular HxH in the west was before the anime, but Jujutsu is probably following that pattern of growth. Chainsaw is like Berserk/AoT with extreme violence and shocking factors so it clicks easier for western audience who likes mature manga, whereas Jujutsu is just seen as a "darker battle shonen" to most who've heard but not read it.
Also, places like reddit upvote most Chainsaw girl fanart to 3000+, so they're just going by "waifu culture" or whatever. Jujutsu's cast is predominantly male chars and the females aren't sexualized. Again, just generalizing based on my observations. I'm assuming people are discussing Chainsaw vs Jujutsu popularity or something. IDK, just my thoughts. I like both, Top 2 in Jump for me.