There are lots of different complaints about the frum publishers, and they don’t all have the same explanation or excuse. Here are some:
1. They don’t print the truth. Explained by the need to cater to their entire customer base. Alienating even a part of the ultra frum community would make it impossible to turn a profit.
2. They print terrible books. If this refers to poorly written and edited novels, it can be because novels are profitable compared to other kind of books. They wouldn’t be profitable if they would require highly talented authors and editors.
If this refers to well written and edited novels without a moral, like those of Yair Weinstock and similar, the reason is that they are perhaps the most profitable at all, but only Artscroll pretty much can afford to create that product. The reason they don’t have heavy handed morals is because that would ruin the books.
3. They don’t print enough hashkafah/torah type books. That is because these books are almost always money-losers. When you see them, it’s usually because the author paid to publish them. And even then, they take up valuable retail and warehouse space.