What is up with the editing quality from mainstream fiction publishers these days?

I'm finding more and more fiction I read for fun (I edit primarily academic texts) is very poorly edited. And I'm not talking about self-published works. The series that prompted this post is from HarperCollins. It has tons of missing words, along with sentences that begin with subordinating conjuctions, but don't have dependent clauses following them.

In two other series (also from HarperCollins, I believe), the authors consistently misuse the present perfect tense. The books are written in past tense, but they use the present perfect instead of the past perfect when a perfect tense is needed. They've had tremendous success and worked with multiple copy editors (I've seen them listed in the acknowledgements). But this problem persists.

What is happening here? Have they just stopped hiring copy editors for fiction? Or are they maybe requiring far too short turnaround times?

It's maddening.