I have the same experience, a large number of parked planes and a few flying ones that disappear after landing, both offline and online.
Traffic is very poorly depicted atm, and I don’t know how much of a priority this is to the devs. I suggest you to keep creating Zendesk tickets and upvoting the following thread:
I couldn’t find any thread about offline traffic with more than five votes. Feel free to create one and link it here so we can all vote too.