Scripting has become more common and comprehensive in recent years. For one reason, the back stories have become more complex, and pre-scripted, and certain events within a match have to match that story. Wrestlers are also engaged in more difficult ‘big moves’ now that require better coordination to pull off.
Back in the good old days wrestlers could just get in the ring and wing it, but they were using a limited repertoire that they all were familiar. Any match back then could start with a series of repeated arm-drag take-downs, followed by wrestlers going from side to side off the ropes trying to catch the other one in a back flip, or countering that move. Then they would stall for while. A wrestler like Buddy Colt could chew up ten minutes ducking out of every move, building up heat from the audience, until he managed to get the drop on his opponent. All time consuming, sometimes entertaining, and not requiring much pre-planning.
Now, the idea is to get the wrestlers going at it quickly, and almost every match has a gimmick ending, where outside interference in some form affects the outcome. Clean finishes demonstrating superior wrestling ability are rare. So the wrestlers will have the finish well determined in advance. And the big off-the-top-rope moves have to be choreographed for the wrestlers to pull them off successfully. A splash off the top rope doesn’t need much rehearsal, but if the wrestler on the mat has to jump up and put his finishing move on the opponent in the air, it requires more cooperation.
Scripting also prevents injuries. Without scripting, wrestlers themselves couldn’t be sure if their opponent was selling a move, or had actually been injured. Now they can assume any wrestler deviating from the plan has a good reason for doing so.