I think the answer is - because the software can. And most of the time, the software can be more resilient with a trivial amount resource usage.

If there was a physical device that could filter gas and non-gas liquids that could be installed in a car we would expect car manufacturers to do that.

I have seen software that puts the onus on users to use it correctly "Hey user, don't enter more than 5 items in this list". Because the software can't be bothered. And if the user enters 6 items in the list and the software crashes and the user loses all their work, everybody can point at the user and tell them it's their fault for not following directions. But personally I'd be embarrassed if that was my software.