Prison time for this is madness.
But threaten the executives with prison, and they'll suddenly make sure that the company complies with the law. I bet e.g. SOX would be taken a lot less seriously without those teeth.
Besides that, I don't see a reason why wilful privacy violations should not be met with prison terms. Don't want to go to prison? Don't collect/share data that you're not allowed to collect/share.
Even for negligence, there is precedent to send people to prison, although that usually requires the negligence to result in death. But the scale at which software mistakes can cause damage is often higher than the scale at which mechanical/structural engineering does: A collapsing building kills hundreds of people. A collapsing Equifax database doesn't kill anyone directly, but affects over a hundred million people, and has the potential to ruin their lives (imagine e.g. private Facebook profiles outing people in intolerant areas - would probably lead to a larger number of deaths than most modern-day building collapses).