Fluids in this game are as thick as syrup, the devs know this, they have said they wont change it because it would be so much time and effort to remake the physics they might aswell just save it for a Stormworks 2 or whatever comes next.

Also changeing things now after several years of people making things would make alot of old vehicles unusable whilst also completely shifting how people currently make vehicles. Its just too late for a major change like this sadly.

As queue said, the main reason is more or less that it would invalidate hundreds of thousands of vehicles.