I dunno, to be fair the Vita had its own set of problems. The DS/3DS are in the same segment as the PSP and the Vita, and they have been a booming success. I think the Vita really hasn't made any ground primarily because its too expensive and the games just arent there. The design is solid, as an adult it fits my hands way more comfortably than the PSP did, but between the hardware cost, the proprietary and expensive memory card, and the fact that there's maybe three games i'm even remotely interested in, I just haven't been able to justify the purchase. I think for adult gamers this is a pretty big thing, we *have* the money, we want to *give them* the money, but if the games aren't there than the games aren't there.
Surprise surprise, the PSP was also expensive, used proprietary and expensive memory cards, and had a really weak lineup for the first few years... make of that what you will.