Well, as we all know, the Tories went for Johnson because they knew he was likely to give them a decent majority. And yes it's the absolute responsibility of voters that they chose to vote for him or their Tory candidate in their constituency to enable him to be prime minister.
The Labour Party chose Jeremy Corbyn as their leader and people didn't vote for him or their local Labour candidate and people didn't vote Labour for him to be prime minister.
We can all set up a political party but it's up to the electorate to vote for us or not. This is democracy.