OK I'm confussed? What does it matter that guys are jumping around? I'm guessing you're to young to remember when WWF/E was all one brand and Smackdown and Raw were just shows along with Sunday Night Heat and Saturday Morning Livewire/Mania/Superstars.
Trying to get low carders over on Raw and Smackdown wouldn't work because they'd be squashed by the bigger names. Having their own show gives them a chance to be away from Cena, HHH, and the likes. Personally I agree as far as I'd like to see the WWE vets leave ECW to all new comers, but lets be serious, it'd be much harder to get people to watch unless they kept people like Evan Bourne and CM Punk on ECW for a longer period of time instead of promoting them to Raw or Smackdown.
At the same, as people have said, ECW is a good place to get WWE vets who are just 'there' to give them another breath of life in their career.
As far as your comment on FCW and other developmental areas, true that's what it's for but look at the people that came out of there.
Jack Swagger and Evan Bourne were both in FCW and won championships. They get sent to ECW and are still doing very well.
Manu, Sim Snuka, and Goldman were also in FCW/OCW and all had one some sort of gold (I believe), and Manu even was the FCW World Champion at one point. They skip ECW (or in Goldman's case not spend enough time there) and go straight to Smackdown/Raw. Manu was barely used and then released, Snuka did decent in a tag division but has dropped off the map since going to Raw and Goldman was released.
You say Goldman was released because they didn't like his look. While that is true, he still might of had a job with the WWE IF they had left him in ECW. They had to of liked in him in some way or never would of got a developmental contract much less make it to television.
In the long run ECW is better for everyone, besides you of course, and the cross brand jumping is a nice nod back to when everyone was free to fight everyone.