Bad incentives can suddenly create a larger problem when the context changes, but I'd wager that they were causing less visible problems earlier: if you structure resource allocation so that getting physically someplace early is important, you might get a free-for-all shoving match, but also you might get a fast-walking race which maintains decorum. The latter is still a problem for at least a few reasons (filtering on physical ability, on willingness to take part in a zero-sum game that filters on physical ability, discouraging people from helping others, etc.), but is not a problem that gets reported on as nearly as much as a shoving match would.
I didn't observe this mechanism in events, but in longer-lasting social contexts, where reduction of slack available to participants is usually the trigger that causes them to worsen.
