It's just perception, there was plenty of scandal involving the lower downs when Johnson was PM too (Pincher springs to mind instantly), it's just that Johnson was also up to his neck in shite so it kinda deflected the rest.
Sunak is also up to stuff as well, I wouldn't be shocked that revelations come out when he announces the election. There's bound to be a load of investments he has, that his policies have increased their value, it's not like it hasn't already happened more than once.