Instead, assume that many, possibly even most, are more interested in being punitive out of some warped sense of justice. Though it might cost them a million in legal fees to discourage efforts to fix their DRM which in turn might only preserve a few tens of thousands in sales or other earning potential, they still doggedly chase these "goals". Sometimes, I think, the lawyers even point this out, only to be overruled by top management. This means that legal action can almost always achieve the goal, being that the goal is nothing more than to make their targets miserable.
The likelihood of a non-profit outfit building open source software being driven by a warped sense of justice and the goal of making people miserable rather than, say, trying to make sure they can continue their stated mission and ensure publishers keep agreeing to digital book lending is pretty bold. But sure, why not.
Because those people are, after all, inhuman robots with no connection to humanity? In fact, I'd say that with any group of humans, each additional human makes this more likely, simply because this sort of attitude easily overrides the less-aggressive attitudes of those who don't agree with it.
You seem to disagree because it would be uncomfortable if I were correct, and you'd much rather it be true that I'm wrong.
>trying to make sure they can continue their stated mission
What person over the age of about 5 thinks that because an organization starts with a particular mission that, even a few years in, still strongly pursue it?
Legal action costs lots of money, no matter who you are, and it's slow. Threatening legal action is usually the most successful mechanism to make things happen, even if you have a one hundred percent chance of winning your case.
In many actual US jurisdictions (and presumably beyond), it's such a pervasive problem that there are now explicit "anti-SLAPP" laws on the book against just that.