It's also a difference between keeping a software engineer on staff and hiring a contractor as needed. One is cheaper for the company even if the hourly rate is higher.
The better question is how we can improve the overall security of the software we write, which this article is more focused on. But we understand that there will be bugs, and security bugs even, no matter how hard we try.
Even DJB (of qmail fame) and Knuth (of TeX and TAOCP fame) pay out bug bounties, and they heavily focus on software correctness over large feature sets.