A newer park buying and building at current values would probably end up being far more expensive.
Anything built in Utah is going to have a relatively short operating season and must make all of their money in that short time window. Fewer visits annually = higher cost per visit.
Many of the costs don't cease during the offseason. Insurance, maintenance, property taxes etc.. Maintenance and hiring is probably even more expensive with everything needed to shut down and then re open the park every year.
Even the big amusement parks in the Northeast have milder climates and much longer operating windows. Lagoon is extremely unique in this regard. If it hadn't been built 100 years ago, it probably wouldn't even be financially viable at all today.