I feel like it isn't necessarily the genre, but the fact that a large majority of them start on Royal Road and similar sites (and of course now Patreon earnings paired with that). The drive there is for consistent output to keep the income flowing, and it is probably easier to keep the same story going for years instead of ending one and starting a new one that might not keep the same level of fanbase support. Not having read much on RR, I can imagine the trepidation over starting a series, only to see it flounder and dwindle in updates so that you never get more of the story, is fairly high with readers there. Yet, the beginning to most of these stories is typically the best part.
I've said it before, but RR is like the TikTok of literature. Easily digestible bites of slightly entertaining ideas wrapped in a whole lot of stupid. But no one younger than us wants to read an entire book straight through anymore, it seems. Even the RR books that make it over to Kindle Unlimited, you can see the "ten minute chapter" construction of the entire book easily. I don't think that's exclusive to litrpg, just the "web serial" genre as a whole.
Well, and to be fair, most of this type of litrpg is also based around the new character striving to become that world-bending superbeing they saw once, and that's gonna take a while just by default, so it is easy for the author to stretch it out in the name of (somewhat) consistency. Some of those mega cultivators in DotF didn't reach that level for millions of years, but Zac will get there in a few hundred or thousand at most even with the artificial slowdowns, but that still could be dozens of books.
There are a few litrpg books that have satisfying endings, but other than Murderhobo I'm drawing a blank right now. I'm sure others will have ideas where I'm forgetting.