There's the metaphysics problem in that all models are wrong. There's more than one competing version of physics (as will help you read Asimov's argument/rant). There's many valid ways to interpret "why" something happens. Physics is trying to understand the causal change of events so that we can generate a model that makes strong and accurate counterfactual predictions. Were that type of model "complete" would we have answered "why" things happen? Depends which "why" you're asking. You could still proclaim, as Fesser notes, "that's the rules God made", which isn't meaningfully different than "that's the way it is".
As for the PSR I'd claim everything does happen for "a reason". But is that reason always knowable? Certainly not. And arguably my namesake proved that there can't ever be any fully complete physics model.
So why be careful? Because my responses are limited, you must ask the right questions. ;)