I don't think Portland is mentally weak or psyched out or all the things fans generally say about their team after a disappointing loss. It's been a mix of poor play and the Warriors having a higher gear on defense that they can switch to when they feel threatened. The Blazers don't have the personnel to beat what the Warriors are doing when they take defense seriously--that's the whole point of this thread. Green is a trap-buster...he's fantastic at taking advantage of 4-on-3 opportunities. Portland doesn't have a front court play-maker who can help Lillard break trapping defenses.
Lillard isn't the problem. He hasn't played particularly well since the Thunder series, but he's trying to carry the offense by himself against defenses designed to stop him from carrying the offense by himself. He's not a transcendent superstar--he's not on the LeBron/Curry/Harden/Durant/Giannis level. He's a star, but he's going to struggle when defenses can focus on him and not worry much about anyone else. Even his nominal sidekick, McCollum, is playing really poorly.
The problem is that Portland isn't built to beat an elite team. Elite teams have the personnel to scheme to take away what you do best and you need to have alternate win conditions. When Lillard is taken away as a scorer, Portland has nothing else it can pivot into, so it just ends up spinning its wheels in a bunch of inefficient actions. Stotts isn't a creative mastermind, but without more play-making and shooting around Lillard, his hands are somewhat tied anyway and Portland will continue to be a good team that racks up wins against other good teams, mediocre teams and bad teams but gets jammed when they face great teams in the playoffs.