A few days ago, the guys from Cupertino launched the iOS 12.4.1 update, motivated by a security problem that had been detected and that made iOS devices vulnerable prior to the iPhone XS, XS Max and iPhone XR to the jailbreak. Coincidentally, this security bug had been fixed with the release of iOS 12.3.
However, when iOS 12.4 was released, this security bug that made devices vulnerable to jailbreak, it was available again. To this day, when more than a week has passed since the release of iOS 12.4.1, the previous version, iOS 12.4 is still being signed by Apple's servers.
The reason why Apple continues to sign iOS 12.4 is unknown, but it is especially striking. While is true that the jailbreak has stopped being what it was a few years ago, we can still find a very active community in this field, although logically it is not as wide as in the past.
Furthermore, Apple is aware that users value safety that your device can offer them and they do not want to compromise it at any time by making use of third-party applications that can put at risk not only the security of their devices, but also the operation of their terminal.
When it comes to a major security issue, affecting millions of users around the world, Apple quickly releases a new update and after a few hours stop signing the previous versions that are susceptible to the problem that has been detected.
In this case, the problem appears to be it only affects the possibility of jailbreak on the device and does not involve any security problem that may affect the stored data, hence, to this day, the guys from Cupertino continue to sign the iOS 12.4 version of iOS.