By no means is this a criticism of Stern nor the quality of the individuals that work there (I don't know them), but developing, for lack of a better term, anti-piracy technologies into their systems would require an extremely high level of both hardware and software engineering, in addition to a significant expense for them to do so. Not to mention, the complications that could artificially arise that would require additional tech support. Then there is the constant, never ending, back and forth of addressing hacks of their security each time it is cracked (and it will be).
I assure you that people who know how to develop such technologies are highly compensated, or if there are security technologies that can be licensed/outsourced they are quite expensive. Quite possibly Stern has done the analysis and determined that going down this path is just not feasible. However, that doesn't mean that they have given up. Rather, they just approach the issue from a legal perspective. In other words, they issue warnings, change EULAs, and make it clear there are legal consequences (assuming they act on them) for anyone violating their IP stipulations. I'm sure at some point, there will be someone or some entity that is made an example of. Typically doing this once or twice is enough to deter the vast majority of others from doing it in the future once they see the true consequences of such actions.