* A memory hog
* A bandwidth hog (its really inefficient about network usage, and uses a lot of bandwidth even when idle)
* Has much lower call quality (a consequence of the above), just try having a call in Hangouts or Skype and notice that Hangouts has much lower audio lag, doesn't kick out people constantly even when screen sharing, etc
* Is now owned by Microsoft
* Never cared about privacy or security (not that Hangouts does, but Skype just sets a very very low precedent)
* Group Messaging is a mess
* Individual Messaging is a mess
The list goes on and on. Its 2016, and "Let's Skype" is not cool anymore. There are much better options available.