Facebook should be heralded for using a real user engagement metric in the advertising reach numbers. They could claim every registered user as a "user" but then they'd be lying (like most other services do).
Given the near total saturation in the US, it's not surprising that their monthly actives are starting to show some decay from the quality of installs going down as they grow as well as some seasonal affect.
Basically, the replacement rate of new installs in the US is lower than the number of people who have not been active in the past 30 days. If we had more granular data, I'd be willing to bet the loss is primarily in users who installed recently, not longer-tenure users losing interest or switching services. Like my mom.
Given the near total saturation in the US, it's not surprising that their monthly actives are starting to show some decay from the quality of installs going down as they grow as well as some seasonal affect.
Basically, the replacement rate of new installs in the US is lower than the number of people who have not been active in the past 30 days. If we had more granular data, I'd be willing to bet the loss is primarily in users who installed recently, not longer-tenure users losing interest or switching services. Like my mom.