I would hazard a guess that it may be because a large number of the electorate in these democracies are easily led, (I was going to say shallow and fickle, but refrained :wink:) and would never stick with a politician that has a high level of conviction and integrity ?
Someone who's ego is so enormous that all sense will be overcome as they put themselves forward to 'rescue' the complete cluster**** that is now brexit. All the others will take a large step back for a while.