Frontlines is 24v24v24, so imagine Player 1 - Player 19. Imagine you have 19 targets stacked, then 4 enemies show up and cast conal Area of Effect (AOE).

What AOE damages who in the stack? If the targeting logic is good, ideally lowest health enemies are targeted first or squishier targets before tankier targets, people may die but the only way to guarantee any one person is hit would be targeting them.
Since there are 19 targets stacked, clicking may be ineffective, we have to tab quite a long list of people... ugh.
Are low health targets receiving AOE damage before higher health targets? Are ranged taking AOE damage before melee because they take more damage? Is it based off distance? This requires all sorts of new balancing and weird interactions that are not as intuitive as area of effect is area of effect.
Capping AOE will require all new targeting logic, it may be less intuitive than uncapped AOE, and it would make grouping up tightly have no meaningful weaknesses. A more realistic solution to problematic AOE is reducing range or damage rather than reworking how AOE works.