Are you going to pay for the extra people to do this?
If not, do you think it is fair to divert effort from the more recent versions to support your version?
forge-1.16.x has been supported for about 22 months, which is nearly twice as long as Mojang supported the vanilla version.
Try getting Mojang to fix a bug in 1.16.5 that isn't a security issue. 🙂
NOTE: I am not associated with forge and played no part in this decision.
The above is just my opinion based on my experience with how limited resources get deployed in software projects.