Many modern planes do have satellite uplinks, but they're mostly used for sending short text messages. Primary voice communications are still over VHF or HF rad

Many modern planes do have satellite uplinks, but they're mostly used for sending short text messages. Primary voice communications are still over VHF or HF radio. If you're having a mechanical problem, the pilot is going to be more focused on not crashing than composing an email. (There are some automated logs that are sent too -- and these were actually used as part of the Air France investigation -- but this is primarily for maintenance rather than real-time tracking.) Even ignoring fancy telemetry systems, planes are normally equipped with an emergency transponder (ELT) which activates if there's a sudden impact. That signal would normally be detected by a Cospas-Sarsat satellite within 1-2 hours. In this case, it's possible that the transponder didn't activate, or the signal is too weak to be detected due to being underwater.