I think they're doing pretty well selling themselves as a "coin for the business world". The pumps came every time when they released another version of their "private" blockchain.
PoI for small coins is a pretty good idea as it encourages getting listed on exchanges and other service providers which can profit from it. But regarding the long term, this algorithm is encouraging using blockchain space which is the scarciest thing in a cryptocurrency (as we see with BTC now).
Another reason is maybe that their ICO was much more successful than NXT's and they've many bagholders that can make some noise and marketing.
For me, NEM is not a bad coin, but if they don't advance their feature set to solve really important issues they will never see mass adoption. For now, it's all speculation (like with >90% of all altcoins).