Yeah, I agree. It's not an issue of can they. They can do anything they want. They could continue them as an alternate, or parallel universe. But they won't. Other than a few standalone stories (like Duane's Rihannsu novels) the novels are usually expected to be consistent with canon. Once the Picard show came out and scattered the current litverse they were over.
But it's more than that really. It's also marketing. As much as I hate to admit it, it makes marketing sense. They're not even putting out a book a month anymore. And even if they were, S&S wants to capitalize on shows that are currently running, not on shows that ended 15+ years ago at this point. There will always be original series books because that's the basis of all Star Trek. They're in it to make money and it's more likely two Star Trek Discovery books will make more money than one Discovery book and one Deep Space Nine book tied to a 20 year continuing storyline.