Last time I lined up 5-6 interviews (after easily 4x applications) only two turned into interviews, one final round that ultimately became a rejection.
I couldn't tell if it wasn't a fit or if I just sucked.
It's just an abnormally bad market right now and companies are passing on good candidates left and right. I highly doubt it's all you.
For the market, your hit rate sounds good. You don't suck, it's just like that out there at the moment. The fact that you made it to a final round means someone clearly thought you were capable of doing the job.
My best advice is if you have any niche skills try to capitalize on those. Your average Java/.NET/JavaScript developer role is seeing literally thousands of applicants. The more you can get off the beaten path the better. If you know some less common programming language or technology you may well find you have better luck searching for jobs looking for that even if it's not your core competency.
Start sending out an application per day. Eventually you'll find you can do 2 per day, 3 per day, etc.
One day you'll have sent out 100s of applications and get proportionally more interviews (assuming the base rate holds).