Very strange as his personal ratings are historically low. Perhaps the others don't want to be associated with such an inept campaign and are refusing to prop him up.
The MRP polls have reflected the lower turnout by predicting what they think it will be in various consituencies. All the polls reflect the data they are using including likelihood to vote - I think all are anticipating a lower turnout.
The new yougov MRP poll for sky suggests Labour will only have a 194 seat majority. This system gives a constiuency by constiuency extrapolation for those nerdish enough.