They use browser fingerprinting. Not only do you need a new IP address, but you need to make your browser characteristics look sufficiently different from anything you've used before (including all metadata that your browser sends to Reddit.com like OS, time zone, CPU, GPU, etc). Otherwise they will re-associate you and ban your new account. It's annoying as fuck.
I still have no idea what they banned me for. Spez is on record saying it's fine to create a new account as long as you don't repeat the behavior that got you banned, but their actions say no, you're banned for life and there's nothing you can do.
The effort required to get back on Reddit is just way to high for day to day usage, so I just stay on here mostly. I still read Reddit for niche stuff from time to time, but yeah it does suck to just read and never be allowed to comment.