IIUC, Bowling Alone pointed the finger at TV. If you looked at time-use surveys in the 50s, versus when Putnam was writing in the late 90s, it looked like TV watching had eaten much of the time that used to be spent doing IRL social activities.

TV was one factor, along with migration/ commuting, two-income households (and now divided households), and more generally that boomers were more individualistic, though he didn't explain why really.

Those , and other factors are more influential than facebook. If anything, facebook helped remote friendships stay connected ( better than phone, letters).