But I'm not saying that it is simply reprinting old material - and I already corrected you on that. I am saying that it is mainly reformatting, repackaging, and rehashing old material (which is also different from "reprinting"). There is a big difference between simply, which means only, and mainly, which means "for the most part, but not entirely."
Well, ok. But still - I don't think either of the Heroes books actually qualifies. The bulk of the content is new. Now, you seem to be saying that this isn't the case because it is a rehashing of older material - but the same could be applied to all the Power books. The PHB2 and PHB3 are the only real 'new' player content books, by that standard.
Regardless of to what degree Essentials actually provides new material, from what I've seen so far it is not enough for me to buy everything, and it is also not enough for me to not feel disappointed in WotC's output over the 7-8 month period in question because not only is there a relatively small amount of actually new material, but it is included in reformatting of old material, and it is almost entirely new "crunch" with little to no new "fluff."
The thing is, I think the last part is more important than the first part. There is new content. What is lacking is flavor-heavy books with lots of fluff. That is absolutely true. That is a legitimate complaint. It is just a very different one than what you were presenting at the start of this thread.
Anyway, I'm not trying to step in and say you can't complain about WotC's current product line or be disappointed in the lack of products you like. I was just trying to point out that some of your statements - that the material coming out was solely "reprinting, reworking, and rehashing of old material" didn't actually ring true to me.
To answer the actual question you ask, though... Why would WotC feel this was a good idea, to launch this big line and potentially leave current customers somewhat in the cold...
In the end, I imagine they thought it was a good idea because that is what their research said, and what their designers suggested. A big launch of the Essentials line might have seemed more likely to root new players in the game while still producing enough to keep most current players interested. That doesn't mean it will work out that way... but I imagine that they did have legitimate reasons for focusing entirely on Essentials for this period, rather than diluting the launch with other products that might have thrown off new players.
Time will tell how successful they will be, in the end.