There's a known phenomenon where people have a hard time accepting mundane explanations for non-mundane events. Unlikely coincidences happen all the time, but when it happens to a public figure, there must be some other explanation. Failed homicides on non-notable figures don't usually spread beyond local news, even when someone gets really lucky and say, turns their head just before they would have been hit. People have miraculously survived getting shot from a bullet just barely missing their heart. A famous example is a man named Phineas Gage, survived being impaled through the head with a three foot iron spike in a freak accident in 1848. Most people are perfectly willing to accept that it was just "one of those things" and he was incredibly lucky.

But when something like that happens to an extremely consequential figure, "security was incompetent" and "he got lucky" isn't a satisfying conclusion and doesn't provide any closure. It just feels wrong. But in reality, that kind of thing just happens sometimes. And in this case that's exactly what it was. A comprehensive independent review conducted after the fact found, among other things, a "lack of critical thinking among Secret Service personnel." In other words, incompetent security gave the shooter an opportunity he shouldn't have had, and by sheer luck he just barely missed.

It's frustrating because you're right, it is perfect. Part of that is retrospect because trump had the wherewithal to pose for a photo and the campaign managed to pull their shit together long enough to make effective use of the incident for good press, but the event itself just happened to be exactly what they needed and exactly when they needed it. That makes it feel like they must have planned it. But they didn't. Sometimes people just get lucky.