The problem is that the "limited range" isn't always part of the intended difficulty and it started to create problems. Fights like P4S have Curtain call where the limited range is part of the intended difficulty as it gives consistent time lapses where players can play around buff application and using mitigation to reach everyone, which is nice because during uptime the 2m meta and mechanics wait for no one, but in other recent fights, like TOP, that is not the case and have some phases that may ask players to randomly go away without them having much agency to play around that limitation. These changes are made to solve that problem which was pretty clear an unintended difficulty.
There is also the whole issue of the hitbox of the bosses which may cause tanks to miss dps buffs or mit if there is any mechanic that force the players to not enter the hitbox and the boss is big enough