"Starship Troopers" (movie) was not based on "Starship Troopers" (novel). It started out as a completely independent project (before Verhoeven was hired as director), until someone pointed out the obvious similarities to the book. Only then did they acquire the rights, and named the movie after the novel, mostly to avoid plagiarism charges.
That said, I find the vehemence of fans of the book to slam the movie disturbing. The book is not very good. It IS boring, I don't think it works, I don't know what Heinlein's point of it was, and has (for a German like me) a creepy fascist undertone, which prevents me to recommend it as YA lit. It's no wonder that Verhoeven pushed the movie to be a satire. And it works.