People do things based on motivation. People motivated by pride and passion know that their work reflects upon them, so they have an incentive to care about quality. People motivated by money know that their paychecks will keep arriving as long as they keep meeting a minimum bar, so they're not incentivized to care about quality, but they are incentivized to care about responsiveness and consistency. For critical software, adding in legal liability for one's work creates the quality incentive that's lacking in most professional roles, while retaining the accountability that we can't expect of volunteers.