I wonder if it is also partially due to family structure in many western societies. Around mid twenties, it is generally expected to have a job and have moved out. Many move away from family and friends due to work/university. Or just live far enough away (but in the same city) that it makes it harder to have regular contact. Combined with the later average marriage age (from low twenties 40-50 years ago, now to late twenties to early 30's), as well as overwork/poor work life balance, people don't have the time/energy or even the means to socialise as much and create meaningful connections to others.