The point of a jury is to get people who are unbiassed to determine guilt or innocence to help make the trial fair and not a kangaroo court. The jury determining that they absolutely did it, but the law is bullshit so they shouldn't be punished and submitting a not guilty verdict anyway is basically a glitch or an exploit. They're not there to determine the validity of the law, just whether or not the law was broken.

Following is a generally devil's advocate point here, because in principle I'm wholly supportive of jury nullification:

The idea of the jury being able to cast verdicts on conscience rather than just evidence does also, however, risk personal bias influencing trials regressively. It is not unknown for systems to acquit or convict someone based on racial prejudice or media coverage of a case, which is why even a sniff of conscience voting of any kind is heavily policed.

There's a whole host of selection processes that try and limit bias in trials while keeping the state from totally controlling the process, but jury duty is one of the only examples of direct democracy under most neoliberal capitalist systems; that comes with all the risks and caveats that it would when applied to any other aspect of our social and political existences