I get the feeling that there's one of two things going on with the REBELS basic figures.
1 - There's a holdup in the distribution chain. And it could be anywhere in the chain: shipping from HK to North America, or from Hasbro's warehouses on the West coast to the retail chains.
2 - There's a street date on the REBELS figures.
As for the limited nature of the REBELS line so far? I get the sense that Hasbro is playing things more conservatively. THE CLONE WARS animated series started out with great ratings as well as a feature film. But ratings and interest tapered off with time. As did sales of the 3.75" figure system.
What does Hasbro have to gain by holding things back? Interest. By delaying the release Hasbro might be trying to ramp up the level of interest in the line, albeit artificially. There's also the nature of the way this new series will play out. There are about 8 central characters, plus troopers. That's very different from the broad scope of THE CLONE WARS. In CW you had LOTS of Jedi, LOTS of Clones, and LOTS of Seperatists. And that had the potential to generate a figure line that might have some 40+ figures per year. But REBELS is different. It focuses on the crew of The Ghost, who are 5 people plus a droid. The Imperials in the series will generate some characters for the line, but we're not likely to see the widespread individualization with troopers that was a big part of CLONE WARS.
I think we'll see more REBELS offerings at Toy Fair '15. But with Episode VII some 14+ months off from release now, I think we're likely to see a rampup from Hasbro that leads towards the new movie. And REBELS is likely to be an interesting sub-line. Kind of the way the late ear POTF2 CommTechs were in the EPISODE I days.