Same answer: Price.

People try to separate headphones which frequently will result into calling lower end headphones worse.

KHP30i and 40 are two of the best bargains. Sennheiser 560s seem to be a great stopping point for some where the performance is good enough forever.

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Ranbling: No need to step further than, in my case Sony M1ST with Yaxi Pads and Neumann NDH30. If I go further I will never listen to music anymore because I can not decide what is the definitive sound I want to listen too.