There are multiple factors: the Mt. Gox insolvency and bankruptcy, the over-saturation of clonecoins, a lot of newcomers looking to get as much as possible with short-term gains, and Scrypt ASICs.
Don't get me wrong though, the profits right now are still pretty comparable to a year ago.
That said, don't expect to make ROI that quickly in general in the GPU mining scene.
Everyone is talking about them but are there really asics 4 scrypt on the market capable of killing gpu mining?
I should clarify and state that I think the current affect in the mining realm is that people are starting to consolidate costs in anticipation for the more powerful ASICs that are possible to be produced within this year; so that is affecting mining.
Currently, at the moment, there are Gridseeds, which are pretty solid (300 kH/s at 7 W/h) overclockable to 400 kH/s but I wouldn't say that those are enough to "kill" GPU mining for Litecoins and its clones. However, I feel fairly confident in at least one of the other major designers producing sometime this year. If (and despite my confidence, there is still a modicum of doubt) everything comes to fruition, that's looking at a possible influx of up to 200 GH/s within the first few waves.
