There are a number of factors on why a film's budget might end up skyrocketing. I might want to talk about it in the future but here's an article that might give you a general perspective: https://www.investopedia.com/financial-edge/0611/why-movies-cost-so-much-to-make.aspx#:~:text=Hollywood%20is%20a%20big%20business,and%20special%20effects%2C%20and%20marketing.