Its been a while since I've seen the movies, but didn't they "plan" out the stunts by doing shitty stick figure drawings? So clearly writers are not needed. Atleast half of the budget probably goes to medical expenses
Movies like Jackass see most of their money go into safety procedures that we can't see, paying to retain lawyers incase something goes wrong, ensuring that they have the rights to film where ever they need them, covering any collateral damage and insurance actually. The rest goes towards paying the crew. "Materials" are pretty damn low.
I did a bunch of research into it years ago after rewatching the movies with the GF and she asked how much work really went into it. It is kind of insane how expensive making it safe and legal really is. They also apparently spend a lot of money talking with lawyers to make sure nothing they are about to do is illegal or can fuck them later, something YouTube prank channels and IRL prank streamers don't do, which gets them in trouble on occasion.
The whole "prank movie" genre moved onto YouTube and Twitch, hence the lack of it on TV, and most of those online YouTubers and streamers are actually breaking a shit ton of laws a lot of the time, and they probably don't even realize it. Many of them film in locations that require all parties to consent to recording (if you don't know what that means, it means that in many places pulling out your phone and recording something is a crime. This includes recording the police in many of these places, and if they decide they want to fuck you over for being difficult it is one extra thing they can slap onto the charges against you to make your sentencing all that extra bit more annoying, it also means someone can go after your ass if they find out about your video and you didn't consent to being in it), and since the "pranks" are often being ass hats in public, that means they don't have consent most of the time making the very videos themselves illegal. It also isn't too uncommon for them to be done in places where filming without permission is a crime, and show acts that are, on some level, illegal. Usually due to property damage or disturbing the peace, but sometimes for other reasons. Seriously, people put illegal shit on YouTube all the time and don't even realize it.
Not many people are going to raise shit over a YouTube video though, but a movie being sold in theatres and on DVD or broadcast TV? Yeah, they are going to raise shit over that, they think they have more to money win with that one. Apparently an important and expensive job for the Jackass film crew during the whole Bad Grampa thing was hunting down everyone who they caught on camera before they got away and getting permission to actually use that portion of the film without any legal BS. That's where Jackass money really goes. Dumb shit normal people would never think of, but they need to be very concerned about.