Wikipedia article about the friendship recession: the documented decline in close friendships and social connections, particularly among Americans since the 1990s. Data shows people have fewer close friends and spend less time socializing than previous generations.

Possible causes

• Bad urban planning which led to the destruction of inexpensive third places.
• Economic factors: as the value of wages have stagnated, people may choose to focus on work instead of investing time in friendships.
• Increased technology and social media usage: there are links between heavy social media and internet use and fewer friends and time spent with others.
• The COVID-19 pandemic: people were forced to limit their physical contact with their friends and could have lost touch.

The article also touches on the heavy health impact of loneliness. Interestingly enough, the article is rather light on details and has only been translated to one other language.

Update: Nick Gray created a dedicated website on the Friendship Recession. It is well worth your time.