To get your legal costs refunded after winning the case, you still need to have the ability to pay them initially - without being absolutely sure at that point that you'll get the money back afterwards. So even a mechanism like that doesn't necessarily always work.

I'm not really sure what precisely is different about the system here that prevents this sort of thing from occurring. Partially it's about culture and people just not having the habit of launching lawsuits like this, but that wouldn't stop a determined troll from doing it anyway. I suppose there must be some sort of mechanism where something like this would get squashed even before going anywhere or generating legal costs for the defendant, but not sure how it works.