> Just guessing: smaller and broken families, more time behind screens, less male-only and female-only spaces, more mobility.

For the first two: the US divorce rate was at its near peak around the time that the linked article's poll shows that male friendships were at their high mark[1]. The average US family size has also not changed significantly since 1990[2].

Put another way: there were more "broken" families in 1990, at a time when the poll says that more men had closer friendships, and the average family size hasn't swung in any direction that would suggest any relationship.

[1]: https://ifstudies.org/blog/the-us-divorce-rate-has-hit-a-50-...

[2]: https://www.statista.com/statistics/183657/average-size-of-a...