Let's take one of the most disastrous bugs in recent history: meltdown.
Speculative execution attacks inside the CPU. This required (in Paul Turners words): putting a warehouse of trampolines around an overly energetic 7-year old.
This, understandably took a lot of time, both for microcode and OS vendors.. it took even longer to fix it in silicone.
Not everyone is running SaaS that can deploy silently, or runs a patch cadence that can be triggered in minutes.
I work in AAA games and I'm biased, we have to pass special certifications to release patches, if your publisher has good relations, waiting for CERT by itself (after you have a validated fix) is 2 weeks.