They might not have even realized they could choose not to support the law, with impunity. Jurors are often given demands like "you are bound by the oath that you took at the beginning of the trial to follow the instructions that I give you, even if you personally disagree with them" that lack any constitutional basis, and the judiciary does its utmost to prevent jurors from even hearing that nullification is possible (much less any arguments in favor).
The judiciary behaves as though those people are very rare (otherwise this wouldn't be so drastically censored), and they're probably right about that. Voir dire filters out many of the well educated, and I wouldn't expect many of the other jurors to figure out from scratch "hey, if I refuse to convict, they can't actually do anything to me" or bet their freedom on that. I doubt I would have before I read about it....
