^ they also have had years of experience with other companies, and they just weren't fresh out of college and say, "HEY! I wanna make my own company!" Then all of a sudden, BAM they made thier first roller coaster 3 years after they first formed then thier 2nd a year after the success of thier first.
You also have to remember that the market for roller coasters is contantly rising and falling, and when it falls, it could mean the end of you. For how long do you think parks are going to keep packing coasters into thier park year after year after year? YEs, there are some parks who have the room and money and they don't have to consider that, but generally most parks fall under the catagory of where they don't either have the space or the money to put out a coaster regularily, and as parks fill up, your going to have to hope that they can find ways to put in another roller coaster, or you need to expand your products from just coasters to like flat rides, family rides, or other things of that nature. Its not just engineering that you are doing, but you are also running a buisness, and part of running a buisness is evolving with what the current intrests of your customers are.