Been wondering the same thing. I think the ENG staking rule is very loosely regulated (if at all).
I bought some ENG on the way down at .8, .7 ... may pick up some more up at .60. The main thing that worries me about ENG is that demand for the tokens are down so much because hardly any tribes/tokens are coming about these days.
I think it is an 'if at all' at present, and the driver for collecting them (for me anyway) was that tribes would be required to vest them depending on services/stakeholders.
As you say though, new tribes are not appearing in numbers and perhaps people are selling in anticipation that SMT will take over, reducing the need for ENG?