Indeed, it did a 16x a couple of months ago and looks like it might overtake dash. Dash is the better chain so I would see that as a signal to sell decred and buy dash. Saying that, 1000 decred earns more money per month than 1000 dash.Decred , a once upon times "garbage" coin , has now similar marketcap with Dash.
Is it maybe because of the low proposal fee?
I don't think it's lower fee is the reason for it's success but they do believe their proposal system is more robust than dash's. Decred to me, however, feels a bit too centralized / censored.
OTOH, they do have a massive $111M treasury! https://dcrdata.decred.org/treasury?chart=balance&zoom=ijhhasg0-kmbjr4w0&bin=month
In this context, I'm not sure how anyone can say dash's proposal system is working at it's optimum.