There's another side to the mechanical keyboard community that is focused on ergonomics [1]. I personally use a Kinesis Advantage 2 [2] with an Adantage 360 [3] on preorder. These are not marginal improvements to my quality of life, they enable me to continue using a keyboard at all.
As for the very expensive, mostly standard layout keyboards... it's an expensive hobby with marginal improvements at best, but the same could be said about furniture purchases. Most people don't choose furniture based solely off its functional characteristics. They want something pleasant to look at, especially since it's something they're using every day for a long period of time. I think there's plenty of utility in that, though personally I would never pay the prices that these people do.
[1] https://www.reddit.com/r/ErgoMechKeyboards/