Well, as I said, it's because they don't really know what to do with him now and they don't lean into what made him cool in the first place. Instead, they lean hard into things that are part of his origin but which shouldn't dominate every Cable story because they are -- at least IMO -- some of the
least interesting aspects of Nathan Summers as a character. Those things being time travel and his techno-organic virus.
Think about it. Starting about 15 years ago in 2008 with the Swiercynski series (which I loved at the time by the way), they shunted Nathan off into the future to protect and raise Hope. Great story, with great art, and well received. But what else did they do at the same time? Well, the X-men still needed a more violent pro-active wetworks squad, so they gave X-Force to Logan to run as field leader. And that Kyle/Yost run was really popular, and that begat the acclaimed Remender Uncanny X-Force run which many modern day fans look at as
the definitive X-Force run. So basically Cable lost his team to Logan, as the Logan led teams are more popular and sell better. Leading X-Force was part of Cable's raison d'etre, if you will... at least in the beginning... however even without it he has shown he can thrive on his own as a solo character as he did in the 90s and early 00s... with the Loeb-Churchill, Joe-Casey, Tischman-Kordey runs as well as Darko Macan and Kordey on Soldier X. Followed by Cable-Deadpool, which is still a cult classic and really defined those two characters in the 00s. Also, he got moved up to the varsity and was on a few X-
men teams. Notably the Claremont-Kubert Uncanny X-men team during the Revolution era as well as Mike Carey and Chris Bachalo's awesome "Supernovas" run on adjectiveless X-men. So Cable showed he could work as both an X-man and a solo character if you leaned into who he is as a character and what he brings to the table versus just some recycled, stale aspects of his origin story.
But from about 2008 onwards, that's all we've gotten pretty much related to Cable. He's the guy who jumps through time and whose powers are constantly on the fritz because his T-O virus is always acting up like a futuristic case of herpes. IMO ever since they brought him back after Second Coming, in Avengers: X-Sanction just before the AvX crossover, they have just not known what to do with this man. The Dennis Hopeless Cable & X-Force series, which was fun, leaned into his powers being on the fritz -- and him having no T-O virus for awhile -- in an interesting way. By giving him limited precognition, and the Spurrier X-Force series (which was a commercial bomb but underrated IMO, and which did "mutant CIA"
waaay better than Percy's X-Force by the way) continued on with this. It was a decent status quo for him, but we knew it wouldn't last. The T-O virus had to come back because being part machine is just part of Cable's aesthetic and original status quo, and most comic characters eventually revert to their status quo after all. Then we got the James Robinson Cable series which basiclaly made him a one-man, self-appointed TVA as "protector of the timestream" or some dumb shit, which his younger self also adopted and used as a justification for killing his older self in Extermination. Dumb shit. And I was glad Duggan called it out as such in Cable #11 or 12 when he brought the older, OG version of Cable back and he lectured his younger self about this and how stupid it was. The Brisson arc of Cable that followed and dealt wtih the Externals was fun, but suffered from some pretty bad art. But it also involved a time displaced Exiles-like team that Cable assembled from various points in time instead of him just recruiting the same characters in the here and now. Which added nothing to the story and felt like throwing in "time travel for the sake of time travel because, well, it's Cable so it has to be included." Then we got a pretty great story from Nadler and Thompson called "Past Fears" but which dealt with... yep, you guessed it: his T-O virus.
To me they just go back to those two wells for every story and it's a bit painful, and it tells me that this X-office (outside of Deniz Camp) doesn't know who Nathan Summers is, what makes him cool, or what to do with the character. It would be like, instead of Logan being a character who can be put into all sorts of stories and interact with all corners of the Marvel Universe, someone said, "no, Weapon X is a huge part of his origin story so literally every single story must deal with Weapon X; or his adamantium, and the fact that it's killing him, so throw in some pain and suffering related to adamantium poisoning and his healing factor being on the fritz too." Literally every. Single. Story. While writers are prone to mine those aspects of Logan's past from time to time, he does a shit load of other things too. Very cool things. Cable can do those things too. Just saying.