Security is always reactive by its very nature. You can do proactive things, but you will always be reactive to novel attacks.
Expect everything to have various levels of rolling upgrades, and soon. That's a lot of work.
When it comes to software it hasn't always been the case. Before the Internet software was considered something stable and even now there are areas, like functional safety critical software, where this is true to some degree.
It's not that it can't be done.
It used to be expensive to a certain extent it will stay expensive, but modern languages, tooling and formal methods will hopefully mitigate that enough.