Personally I think it's a combination of the economic recession and free porn. Also don't forget that in the past the online adult industry brought new innovating things that were heavily adapted by the online mainstream industry.
Now a days there is almost no innovation introduced by online 18+ companies but simply by companies active in mainstream.
In my opinion most of the adult sites are offering all the same and stick to the same business model what made them in the past successful which is not a guarantee to be successful in the future.
Everybody is doing the same, spitting out tube sites to catch those free wankers who probably not gonna buy a membership while everything is for free.
I think innovation on different media, offering high quality content and diversity will be the key to conquer marketshare and make the consumers return
