1. Hyper-perfect social media / television setting "the best" expectations for an event.
2. Decreased knowledge of how to host a gathering. It's not rocket science, but throwing one the first time can seem daunting. And throwing one well does take skill. E.g. icebreakers, identifying and facilitating the right introductions by highlighting mutual interests, making sure wallflowers have a good time, defusing tensions, food, etc.
3. Decreased American tolerance for and ability to handle awkwardness, and there's always going to be some awkwardness in social interactions.
4. Decreased public/accessible American meeting places. There used to (< 2000) be a plethora of low-cost, broadly-accessible spaces that could serve as training wheels for events (handling food, furnishings, cleaning, etc). They've essentially all been privatized, commercialized, and optimized to turn seats -- think real coffee shops disappearing in favor of Starbucks.