If people want to know why Matthews doesn't score on the power play like Ovechkin and Draisaitl do:
That first sequence on the power play perfectly illustrates the problem.
The Leafs simply do not find Matthews for 1 time shots on the power play.
When they pass to him, it's almost always too late and he doesn't have a lane to shoot, and when there is a play to be made, they look him off and go for some stupid move instead.
The power play is so effective when they simplify things and get the puck to players with shooting lanes and then get 2 players in front of the net for screens/tips.