Yeah looked at investor's profit chart of bitvest here https://bitvest.io/charts and it seem there was decrease on nov and dec last year so may be that have forced many to divest their investment on bitvest.

Actually investing in gambling site's bankroll also have risk of losing and profit you can make is really low, you can't earn like 50% or more within one month. But i think in long run house will make nice profit so better not to divest when site have gone through big loss due to some lucky winner winning big.