Did you watch those matches?
Ferrer re-broke a couple of times in those two finals and could have snatched a set IMO but he doesn't have weapons against Nadal.
All Rafa was doing was putting balls into the court for most of these finals and he had a very big safety net in the fact that Ferru couldn't hold serve easily. Simply put, he did just enough and even so one of these finals could have been prolonged by a set by Nadal's slip-ups(being re-broken or in danger of being re-broken nearly every time he broke David).
If David actually had a serve, he could have pushed Rafa more in any of these two finals. He moved great and was almost always into Rafa's service games but was woefully weak on his own. Ferrer broke Rafa 5 times in these two finals but could have easily done it a couple more times if he had played a couple of points better.
Overall,for these two finals, Rafa had 27 BP(11 MC, 16 Barca), Ferrer 15(7 MC, 8 Barca) but their conversion rate was very similar, 36% to 29% in MC,38% to 38% in Barcelona. And it shows in the scoreline of these finals.
Nadal was just a bit better than Ferrer in MC at the end of the sets or else he could have lost a set, if not the match. He always had Ferrer's weak serve to rely on, he really didn't play anything amazing.