As I've previously said about the Newcastle managers appointment post takeover, you don't want to be the first, second or possibly third one as you'll inevitably be dealing with problems.
Truss, or whoever eventually takes over from Johnson, will be a useful idiot to take the flak for the post-pandemic, post-Brexit mess that we face. Anyone with any sense in the Tory party will not want the top job until after that.
In fact, it wouldn't surprise me if the Tory hierarchy were actively planning for a period in opposition while the Libs, Labour or any coalition attempt to clean up the mess. Appointing Truss could well ensure a loss at the ballot box. By the time they hand over power there'll have been more than enough time to have siphoned off enough money to keep them happy in opposition.