they do. it just doesnt work. that little brown dot between your armatar and your name used to turn green when a user came online. it was disabled due to lag issues.
In AG3, theres a feature that allows you to see when a user has been active. Though, some people may have it so only their friends or followers may see it.
There is an online feature on AG3 and it does function well. It tells such as "GhostOfMatrix was last seen twenty minutes ago" "Cormyn was last seen an hour ago" etc..
The one on here doesn't work for the reason Floyd said.