The former is lock-in. The later example is better described as "network effects", i.e. Facebook is compelling to you because all your friends are on there, a

The former is lock-in. The later example is better described as "network effects", i.e. Facebook is compelling to you because all your friends are on there, and the more of your group that engages on the platform the more valuable it is to you and the harder it is to get everyone to jump in mass to another platform.