What I want to know about all these late sequels, is what takes these studios so long? Where were they in the 90's? throw a $150 million at everybody involved sometime in the decade after the last movie came out, not thirty years later!
Unfortunately, we can blame Bill Murray for that one. He outright refused to sign onto decades of proposed Ghostbusters 3 scripts, and being one of the owners of the property he had veto power over any sequels.
That's why they eventually went with the 2016 reboot, since Bill Murray couldn't veto it. It's probably also why they had a ghost kill his cameo in a particularly mean-spirited way. It's also why a lot of people have said that the Ghostbusters 360 video game is the real Ghostbusters 3, since all of the original cast were in it for the final time in a script penned by them.
If this is Ghostbusters 3, I wonder what they said to him to get him to sign off on it.