There are various reasons for this, major one being that the 9800X3D has more L3 cache per thread than the 9950X3D.

And also wrong that a 9950X3D is 2x 9800X3D combined. A quick glance would tell you that, since 9950X3D has 128MB of L3 cache shared between more threads while 9800X3D has 96mb for half the threads, so more L3 per thread.

And most of the times, even when a 9800X3D loses to 9950X3D in games, it's usually within 1-4% margin for most games.

It's a monster for games and some workloads.

It's funny that people who blindly buy 9950X3D for gaming+office workloads without checking benchmarks often end up with similar or slower performance.

Much smarter to use the price difference on other hardware to speedup other things such as faster NVMEs, efficient silent cooling, faster GPUs, etc.