I do know that many players leave the game, only to come back to it with their ports after a year, or a few years.
I've been playing for 10+ years, and I'm sure there are literally thousands of ports that have been 'abandoned' or not played any longer as well. But on the flip side, I know that HSX does not delete ports of players, and there are some ports on the LTD Board that other players have "retired" when they reached $2B, 5B, etc.
No one really knows "how many" ports are in the system, how many of them actually trade on a regular basis, etc. HSX does not release this information.