Everybody loves watching wrestling! If not, the ratings would not be as high as they are! I have noticed that a lot of the ECW roster that is truly talented are wrestling on either Raw or Smackdown as well. The people that need more work are stranded to just the ECW roster.
More and more, the ones that are ready for the bigger shows either hold the ECW World Title or wrestle on the other shows. Matt Hardy for example was placed in ECW on a probationary basis after resigning his contract with WWE. He was placed on a probationary basis because TNA was in talks with him and Jeff Hardy about making a move to TNA.
Mark Henry is a very dominant superstar, but everyone knows that his weight has been a problem with WWE. It isn't because of his "bigness" but because WWE doesn't want him to push himself too hard. The company had to pay him extra to skip out on the World's Strongest Man competition this year and they don't want him to get hurt.
Most of the new superstars in WWE either start out in ECW, like CM Punk, or go straight to a big show because they have already made a name for themselves elsewhere.