It isn’t. When you look at studies they reveal that loneliness is very prevalent in multiple groups of people and in general. In some studies older women are the most lonely group.

Gender and Age Differences in Loneliness: Evidence for People without and with Disabilities

Gender Differences in Loneliness Over Time: A 15-Year Longitudinal Study of Men and Women in the Second Part of Life

There is much activity by anti-feminists in particular to push the narrative that men are the most lonely group and that of course the reason are women. This is heavily pushed by media because people seemingly like that idea more than that gender stereotypes targeting men are potentially more at fault.