You probably don't, they are certainly not for everyone.

I have two of the earlier keyboards (ergodox ez). I gladly paid the price because it makes me more comfortable. I find it similar to a nice monitor or chair.

I don't know if my performance is better, but it's a nice piece of gear that's a joy to use.

If you're like me with RSI and wouldn't have a career without an ergonomic keyboard (I use a Kinesis Advantage), $365 is a rounding error.