Just because you lose a suit doesn't mean the suit was unjustified. You know all those plaintiffs suing the banks over mortgage related issues? Most of those plaintiffs are going to lose, because they can't back up their claims with sufficient proof or the banks skirted but stayed on the right side of the law, at least technically. Should those plaintiffs pay the banks punitive penalties for bringing suits they lost? Should they even have to pay the banks' legal fees?
It's easy to throw around ideas like loser-pays when you have a clearly established preconception of who the "good guys" and who the "bad guys" are. But that doesn't make for workable policy. Bankers/private equity folks, etc, really think they're the good guys and the people suing them are just bitter because they got the short end of a deal they knowingly got into. The folks that work in petro-chem really think they're the good guys, and folks suing them for environmental harms are just hypocrites who want all the advantages of modern petrochemcial processes (pretty much every gadget you own is the result of a horribly polluting process) but aren't willing to put up with the inevitable consequences. I'm sure they'd love loser pays too, for situations where some investor ends up not being able to prove outright fraud, or where some community can't muster the evidence to prove that a chemical plant caused kids to get cancer.
Loser-pays is just a band-aid on what is a more fundamental problem with the patent system: the law has evolved to make patents a strong right with very ill-defined boundaries. That makes litigation protracted and expensive because you end up getting into the weeds of technical issues and whether this kind of thing is like this other kind of thhing that the court system isn't really competent to deal with. No amount of tweeking at the edges is going to fix that. The solution is to make patent rights narrower and more well-deliniated. Shift the focus to questions like whether the defendant unfairly competed with plaintiff by copying the plaintiff's IP instead of innovating themselves. These are things the court system is competent to handle (and has been for hundreds of years). When it can be easily seen whether clearly-defined legal rights have been violated, frivolous litigation naturally diminishes because the cost to prove allegations wrong goes way down, which makes the incentive to just settle also