They have five seasons fully planned out...
http://www.ew.com/article/2016/09/08/westworld-plan
It wasnt about getting the first 10 [episodes] done, it was about mapping out what the next 5 or 6 years are going to be, Westworld actor James Marsden says. We wanted everything in line so that when the very last episode airs and we have our show finale, five or seven years down the line, we knew how it was going to end the first season thats the way Jonah and [executive producer J.J. Abrams] operate. Theyre making sure all the ducks are in the row. And its a testament to Jonah and Lisa and HBO that we got them right, especially the last three scripts. They could have rushed them and get spread too thin. They got them right, and when they were right, we went and shot them.