A big part of the reason is that most of Sun's own sales people desperately don't want to sell it - they want to sell what's selling, and that isn't going to include anything compelling the IT managers they deal with to layoff most of their staff and go back to actually working in IT.
Sun's own marketing reflects and extends that conflict: by labelling the Sun Ray a "client" they contradict the fundamental Sun Ray architecture while burdening the machine with a lot of expectational baggage from the Microsoft client-server world that simply doesn't apply.
So what should they call it? I've been using the term "smart display architecture" for the kind of user controlled system Sun Rays enable since well before Microsoft grabbed the label "smart display" for something that was really rather stupid - producing a situation in which "Smart Display" is the most meaningful label, but Microsoft's misuse of the term has destroyed its value.
So what should Sun call the thing? A talkback comment from p_msac last week suggests a possible answer.
Here's the operative bit:
The enterprise scenario [consists of] a lot of disfunctional and isolated applications, [mainly] from MS, that focus simply on the Desktop PC.
That is why they call it the Magic word: Personal Computer. Not Enterprise Computer.
And [it] is this view of the "personal" computer that costs a fortune to companies in terms of productivity.
Sun already sells enterprise computers, and SuSe offers a software "enterprise desktop", but here's an idea for Sun's Jonathan Schwartz: stop hobbling Sun Ray sales with that "client" label, call it an enterprise something - desktop, display, screen - and sell it in bundles with enterprise servers and enterprise software from partners like Oracle.