Elite Dangerous is older than Planet Coaster. They still update and add to the game. There is a full team of staff working on it. So why would they give up on a newer game that is still popular and makes decent sales? Whether or not, PC2 is on the horizon, from a business point of view, it makes sense to want to maximize on a current title. They wouldn't want to stop a revenue stream until there was something in place to replace it.
It's like car manufacturers. They will continue to sell a certain model of car right up to the launch of the replacement version. Because they are a business and they want to make money.
Also Frontier say it isn't dead, so that's good enough for me until they say different.