I so hard agree with this. There's gonna be 2 major groups of players, I think, and people feel free to correct me if you don't fit into these groups.
A) Players who want to worry about the business side of running a park, who enjoy variable amounts of pressure to make the right decisions during park growth. To me, the fun of a park builder is the ratings and staff management and research, pushing out incomplete genomes to fund further park development, with the ability to change storm frequency or starting funds or disease frequency depending on how challenging I want the game to be or which game systems I enjoy more/less. Players like myself get through the missions, run a sandbox game, and wonder why the heck I'm not allowed to choose a map, have access to all dig sites, and play the game I enjoyed through the campaign without missions or storms or breed restrictions. Why can I even build a science center and expedition center in sandbox?
Sorry for the rant.
B) Players who want god-mode free-for-all play-with-my-toys dinosaur park game have to spend hours grinding out missions with tornadoes tearing up their park and T-Rex being delivered day 1 and escaping to eat their guests. Why? Sandbox is a totally different experience as it exists now, and I don't understand why these two game modes as they exist are tied together at all.
Please, if anyone's out there, I want to love this game so bad but I want a hybrid game mode, where I can scale and toggle systems but keep the sense of work and progression. And those poor sandbox players, just let them play with their toys! Forcing them through missions HAS to be turning those types away, right? DAMN IT