Because they are offering little real value (the vast majority of value publishers really offered was the advance, which I haven't heard of these guys offering, and distribution which you can do as well yourself thanks to Kindle + Nook stores).
The one MAJOR cost left to self publishing if you are truly serious is editing, unless you are in a genre where stock image covers won't cut it. Giving up a % of sales revenue for the rest of time for a book considering the limited help they really offer these days is just silly. Dean Wesley Smith has been discussing this on his blog at length over time.
I don't think it's a matter of the cost of self publishing. It's the benefit of having someone whose full-time job is to distribute and promote your book. Having every single author become an expert in that is hugely inefficient, and it's probably not what your average writer wants to be doing.
Just because you can do your own dental work doesn't suddenly make it a good idea, much less an economic one. For work that's somewhat specialized and very intermittent in nature (like promoting a new book) it's often better to aggregate the labor.
Promotion and connecting writers and editors is not an insignificant value. I don't know what cut they're trying to arrange for themselves, but these are services that the writer is going to pay for one way or the other.
Outside of to Editors/publishers agents aren't currently set up for promotion. Their place has, for a good while, been primarily as taking over the slush pile from publishers plus getting better contracts WITH those publishers for the author. Good agents increase the advance and/or royalties such that the contract is for more than the 15% they take as a cut so you get more money.
Editors they MIGHT have connections with, but so do a lot of indie authors these days, so if you join those communities you can get good recommendations from fellow writers.
Again, "one way or the other".
If a writer doesn't have an agent who provides these services well, writers will have to spend their own time and energy on those endeavors, even if only to cultivate and manage direct relationships to other (editing/marketing) professionals. Many writers don't care to do any of that and can be well-served by hiring on someone else to do it.
Surely, some, or even many, agents aren't doing particularly great. But that's no different than any other provider of a service. Most may suck, but that doesn't mean the whole category is of questionable benefit.
It's actually a huge positive sign that they're at least recognizing the deficiency and trying to reposition themselves. It means they'll be eager to become even better at the things that writers most-need in the new landscape.
The one MAJOR cost left to self publishing if you are truly serious is editing, unless you are in a genre where stock image covers won't cut it. Giving up a % of sales revenue for the rest of time for a book considering the limited help they really offer these days is just silly. Dean Wesley Smith has been discussing this on his blog at length over time.
http://www.deanwesleysmith.com/