After re-watching the game I think there were a few main reasons why the finals turned into a Barcelona monologue.
First and foremost, Spanish midfielders are the best in the world. Some of the best ever may be on the field right now. Barcelona has an emphasis on their youth program and their home grown players like Xavi, Messi, Iniesta, Busquets, Puyol and Pique all are indoctrinated with the Barcelona way of possession and midfield dictatorship. Against a Brazilian side that lives for the quick break, Guardiola stated all midfielders and 3 defenders. Santos had never seen anything like it and the speed of the game and passing mesmerized them.
On the attack, Barcelona became a swirling mass of midfielders orbiting, all exchanging positions and depths and hunting for that perfect pass and run into the box. A cloud of Barcelona shirts hung just outside the area just waiting to strike at the sight of any weakness as the switched the ball back and forth. Barcelona’s goals were scored as players eventually found those gaps and were released behind the defense. The rest was just impeccable finishing.
Finally, as teams trying to figure out what to do with Messi, Guardiola continues to frustrate them. The predicament is that Messi really plays like a midfielder in terms of his distribution to players around him and using them in clever combinations to breeze around defenders. The only way to stop that is to clog up those passing lanes by sitting back with alot of defensive midfielders, which of course hurts your attack and is partly the reason Barcelona has let up zero goals at home this entire year.
But if you sit too far back, and Messi is allowed to run at you with pace, no defender in the world stands a chance 1v1 with Messi at full speed. So the option is to send a central defender (as Real Madrid did) out to meet him early so he cannot turn. Guardiola’s response has been to have Messi drop deeper and deeper, so that if the center defender does follow him, he is so out of position that Fabregas and Sanchez can exploit the space behind him, and the result is the slew of goals we have seen in recent weeks.
The final reason why Barcelona crushed Santos was Dani Alves playing so high on the right wing that Messi always had an outlet. Their combinations were better than perfect, a result of them staying for hours after practice just passing to each other. Alves-to-Messi was at the genesis of 3 of the goals, and is just one more element of their attack that seems impossible to defend.