Without knowing all the rules for AoS 3, cant say why they went this route yet. however it usually is a change made to improve melee combat. much harder to wrap units and stay in coherency, and much harder to get everyone in range of attacks. Adds more skill requirement to melee combat, rewarding players who are good at preplanning and positioning. pile ins actually matter again, and players can and will screw themselves in combat by moving without thinking. some may see that as a bad thing, and others will like it.