I get what you're saying. The fact that using different services leads to a loss of social connectivity since the majority of people use one service is more an issue of the service itself being a monopoly than it is one of herd mentality.

It always goes back to capitalism when the services that become monopolies are the ones that care the least about people, since the services have already reached the "too big to fail" public perception.

EDIT: It's also an issue of some people being too stubborn to accept change unless it is forced upon them by everyone around them