I am split on this.
If you allow it, then you get eevblog sort of posts where there are 1000+ comments over 5 years in 50 pages that switch topics so regularly that every 2-5 pages should be entirely seperate posts and reading them because of wanting to find information on the title topic is completely useless.
On the other hand, sometimes an issue will become stale and someone will comment with an update or solution to a problem and get chastised for "necroing" and sometimes their comment with a solution deleted.
Because making a fighter jet is a more than a decade long undertaking with existing military industrial design, manufacturing, and test infrastructure.
Making one from scratch without the existing IP and infrastructure is an even larger and more expensive task.
It takes the cost (out-my-ass example) from 30 million per jet with a 3 year lead time, to 150 million per jet with a 15 year lead time with an unproven, likely worse, aircraft. And if they are trying to protect themselves from close neighbors' current trajectory turning hostile, they probably don't have 15 years.