People have been saying this for the past 16 years, but the reality is once a system is in production over time it becomes increasingly risky to replace it. Because over the life of a piece of software you make tons of small fixes, resolve bugs, adding customer-specific functionality, etc. that you'd completely overlook when planning our requirements for a rewrite. Which is a big problem when other systems are dependent on the software operating a specific way i.e. APIs, web services, and so forth. Not to mention the economics of a rewrite also has to make sense. Nobody is going to spend 2-3 years recreating what they already had and get no additional functionality out of it. Certain software basically has to get so bad that literally anything replacing it is better than what came before for replacing it to be the right approach.

Just how debian was done after weak keys, OpenSSL was done after heartbleed, or Windows was done after (rolls dice) the print spooler RCE

Not at all. People will patch and carry on.

always was